[core/theme] Add per-module theme override
[core/theme] Add per-module theme override

Allow users to override theme values via parameter, such as:

bumblebee-status -m spacer -p spacer.theme.bg=#ff0000

for a red spacer.

see #223

tobi-wan-kenobi/bumblebee-status,tobi-wan-kenobi/bumblebee-status