Some laptops, such as Dells, may display an unknown charge state when
the battery is attached to a docking station, but discharging (because
of configuration settings for longevity of the battery).
Show that nicer.
Add an option to load a user-specified icon theme (which will override
the theme's icons).
Also, commit a first version of a set of icons from the ionicons set
(see http://ionicons.com/).
see #252
