The blank timeout cannot be longer than the DPMS timeouts,
the DPMS timeouts cannot be shorter than the blank timeout
simply because blanking after the display is already suspended
doesn't make any sense (and vice versa).

in the settings dialog for consistency with other Xfce settings
dialogs.

Add information on 1.3.1 release and prepare for 1.3.2

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.

The new icons are more consistent (in color and style) with Gnome/Adwaita
and the new keyboard brightness icons.

There is no more reference to it in the code, hence it isn't
used anymore anywhere.

Max minutes was limited to 50.

Most parts in the power manager are named in different ways. Let's try
to find a more uniform naming scheme for consistency reasons. This commit
renames the UI widgets. It is only an internal change and does not
effect anything visible to the user.

While more complicated, this fixes the sliders having different length
and positions.

Users can still control the sleep mode via the hidden option dpms-sleep-mode ("Standby" or "Suspend")
The default value is "Suspend" (implicitely set in xfpm-dpms.c)

The exact intent of this feature is unclear, its implementation
unfinished.

Remove all related GUI widgets from the settings dialog.

Brightness handling is usually done by the kernel, so the user should have the
privilege to decide whether power manager takes over the handling or not. It is
not good to automatically take over the handling, break it and then make the user
worry how to get everything going again.

This means we will need more options that will not fit on the display tab anymore,
so create an extra tab for brightness.

As an added benefit, this solves the layout problems with the sizing behaviour
of the sliders in the table.