When running some versions of UPower, the code path had a minor
logic error causing it to never return the "display device". This
patch fixes that check.

Only build in the new xfce_dialog_show_help_with_version function
if the system has libxfce4ui 4.11.1, otherwise use the old help
function in order to still support systems with Xfce 4.10.

The LXPanel plugin API was completely changed in version 0.7.0
without any module versioning or backwards compatibility. This
patch make the plugin work with the new version while retaining
the ability to still build for the old version (based on checking
the package version at compile time).

share/xfce4/panel-plugins has been deprecated in favor of
share/xfce4/panel/plugins.

There are a couple conditions where the plguin would crash or
emit runtime warnings due a device being connected or
disconnected. Those should be fixed now.

xfpm now points to the versioned docs hosted at docs.xfce.org.
This version string will always point to the major.minor of xfpm
so it will auto-increment in future relases.

When the xfconf brightness-slider-min-level is set, the plugin
will now dynamically update the range slider (if shown) for the
new minimum as well as stopping the mouse wheel from scrolling
below that level.

Since the brightness plugin merged with the battery plugin,
rename it to Power Manager Plugin. Also since we support
LXDE we'll stop calling it the Xfce Power Manager Plugin as
a LXDE plugin.

Draw the progressbar indicating the load-status of the devices
with cairo, eradicating the need for an icon per load-status.
TODO: Add the same drawing routine for the devices tab in the
settings manager.

This makes it consistent with the device icons in the same menu.

Patch provided by Simon P.

Clicking on, or dragging, the slider of the display brightness
slider of the plugin menu causes the plugin to crash. This
behaviour has been present since this feature was introduced.

I've tracked down the cause to the way the "value-changed"
signal on the scale_menu_item object is handled. The signal
is defined with a gdouble data item for the range value (but
isn't used anywhere?) while the callback function
range_value_changed_cb isn't expecting this data.

By changing to g_signal_connect_swapped for this signal in
function battery_button_show_menu & swapping the parameters
in the callback function, the range slider is now working for
me.

This makes use of the xfconf property introduced in the previous commit.
Initially, min_level is set to -1, which causes automatic determination of
the best minimum level when the slider is created.

Setting a minimum level other than 0 might only make sense for newer
laptops, which can be heuristically determined by looking at the available
range of brightness steps. Any backlight interface providing more than 100
steps will set the minimum level the slider will support to 5, which is
barely enough light to see the screen contents. The user can change this
via xfce4-settings-editor, or its command line companion xfconf-query.

I still noticed a slow-down on my machine even with the newly introduced
update timer. Increasing it to 50ms is still enough for not causing the
updates lagging behind too much, while filtering enough events to keep
the widget response snappy even with two monitors attached.

Take the x/ythickness into account when setting the size request and
get the closest sharpest icon instead of GTK_ICON_LOOKUP_FORCE_SIZE.
Also, apply some Gtk+ style properties that the convenience functions
of the panel provide by default for panel plugin buttons.

Dragging the slider produces a lot of events, and processing these makes
the UI lag behind because of the many helper calls. Let's update the
brightness level only after a small timeout.

Thanks to Simon for pointing out that a custom menu item would
accomplish what we need and for pointing out the ubuntu app
indicator code that this patch was based on. Additional thanks
need to go to Cody Russell for creating a custom menu slider
widget I could copy.

If this branch gets merged in the brightness plugin will no longer
be required so let's drop it now. The functionality is present in
the battery plugin.

This way it won't show as two different menu items.

This will consolidate the plugins which can then be renamed.
There's an issue where the mouse grab on the brightness slider
doesn't work, hopefully we can do that without making a custom
popup window. Scrolling on the plugin icon or over the brightness
slider does work.

When the GTK theme changes, resize the panel button and its icon.

When the user selects a device in the battery plugin, the xfpm
settings dialog is activated, the devices tab is brought to focus,
and the device is selected with the details shown.

In the battery plugin, there's a chance that we've filtered out
any devices to display and thus there's no need for the menu
separator.

This way the panel icon will increase with the LXDE icon_size
changes.

Adds support for the battery plugin to be built and used in LXDE
as the system tray icon was removed. Thanks to
https://github.com/nandhp/multiload-nandhp as it was used as a
complete example on how to easily do this. There may be a couple
things that need to be added to make this have the same
functionality as the Xfce plugin.

Signed-off-by: Eric Koegel <eric.koegel@gmail.com>

Not sure why one would check for specific numbers instead of ranges?

Signed-off-by: Eric Koegel <eric.koegel@gmail.com>