Set brightness and DPMS related settings insensitive conditionally Previously these parts of the UI were simply hidden, we'll implement an infobar later that informs the user that these things aren't available

With UPower < .99 this patch will make the battery panel icon
dynamic by displaying the ups or battery device with the highest
percentage. This patch also cleans up a couple small issues with
the last two patches (unused function and variable).

When upower reports unknown there is no useful information for the
device so present that to the user rather than a 0% battery level.

Redo settings dialog from scratch and remove unused code Remove trayicon and treeview code, make dpms mode sensitive conditionally Settings dialog now mostly conforms to Xfce's HIG

The 'online' state only works for line_power devices so make the
fully charged state use the charged icon so it's more accurate.

Upower 0.99 supports a composite display device that represents
the state of the computer. When that device type is around we will
use it to determine the panel icon, update the tooltip, and replace
the UP_DEVICE_KIND_LINE_POWER in the menu since it would be redundant.

The left click menu now displays the devices and their status at
the time of the menu's creation.

Rather than using a custom window migrate to custom items in a
GtkMenu. To that end, change from a GtkTreeView to GList internally.

Also put more trace/dbg messages in place so it's easy to track
these issues when upower breaks itself again in the future.

Dynamically changing the icon in the panel itself looks horrible.
Revert and improve it later.