Add initial loading of qt jdenticon plugin:
https://github.com/redsky17/qt-jdenticon
Currently, the library's functionality has not been integrated
into the rest of nheko. Next step is to add a configuration
item in the User Settings and use the plugin to generate
avatars for users without their own picture. These avatars
should be cached in the Cache object.
User colors are now stored in cache. This is consistent
with other similar variables. I think there's a bug
right now where it doesn't properly refresh colors
for the TimeLineItem when the theme is changed.
Author color is now cached so that it will not be re-calculated
each time a new message is posted. This cache gets cleared when
the theme is changed.
Additionally, the author color is now automatically refreshed
when the theme is changed, fixing the issue where you had to
change rooms before the colors would switch.
