Battery widget: show more information

Use the power_supply name instead of an hardcoded string.
Differenciate batteries and AC

Provide a data structure for PowerSupply and functions for AC or battery
management.
PowerSupplies information:

Provides a new API to read/get information about power_supply and
Battery.
refactor a large part of the code and implement configuration
move function in different modules
remove useless things such as process

also, do not show France Time in the default configuration since not-all
the people leave in this timezone.
Fix Power Supply aesthetic

* do not show AC list (no need to create a box for it)
* set a static size of 100 for the levelBar (fix display errors on some
  gtk-templates)