fixes #214

Fixes #180

removed from:
 - emoji panel scrollbars
 - emoji category labels
 - splitter image handles
 - textfield setTextColor impl

small change to the category separator label for better contrast /
readability in dark mode.

removed setTextColor completely from TextField. Doesn't appear to be in
use anywhere, and focus going more toward qss themeing from qproperty
setting.

I'm not sure, if that is the right way, but Qt doesn't really have a way
to format custom localised dates, so I tried to find the closest
approximations to what we currently have.

Relates to #69

Update to mtxclient 0.3.0