This commit adds new settings to some widgets that allows to auto
select/hide them based on their current values.
The cpu/memory/network/storage widgets get a setting that auto selects
the widget if the current value/percentage is over a value.
The battery widget gets a setting that auto selects the widget if the
current percentage is under a value.
The storage widget gets a setting that auto hides the disk widget if the
percentage is under a value.
Also added 2 new settings (auto_select_fill and auto_select_text) to the
theme, in order to select the fill and text colors of an auto selected
widget.
(Easter egg: the network icons change if the value is over the limit)
PR: #1353
