LXDE battery plugin support (Bug 10929)

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.
Fix conditional builds

This patch fixes it so that the many different --enable/--disable
options cause the build to still work properly.
React to LXDE panel configuration change events

This way the panel icon will increase with the LXDE icon_size
changes.
Use gint32 for brightness levels instead of gint where applicable

Probably these gints doesn't cause any problems, but perhaps it is safer to be more
exact here. I think I got all of them now.

Signed-off-by: Eric Koegel <eric.koegel@gmail.com>
Fix two more range checks regarding brightness levels

Signed-off-by: Eric Koegel <eric.koegel@gmail.com>
I18n: Update translation ast (87%).

181 translated messages, 25 untranslated messages.

Transifex (https://www.transifex.com/projects/p/xfce/).
Let xfpm control X11's screensaver extension FIXME: dbus_init in power.c resets the configured values if xfpm restarts
Bind xfconf properties after object is created
Disable screen blanking in presentation mode
Fork before gtk/dbus init

https://mail.xfce.org/pipermail/xfce4-dev/2014-May/030715.html
has the rational for the change.
Fix minor build issues