work regardless of the theme choices the user makes.  The code
now incorporates the contrast between the background color and the
color generated by the user_name when picking colors.  It currently
has two 'big' issues:
1. Colors are not cached.  I am planning on adding a QHash for this
a little later.  This should improve performance by not calculating
the color for the same users over and over and over again.
2. Theme changes do not trigger the colors to get refreshed.
Currently, you will have to switch to a different room and back
to get the colors to refresh.

Add author color generated based on user id.

This fixes #2, but reverts mujx#438.  I do not think mujx#438 was a
valid issue, as it complained about the display of valid HTML on riot,
which speaks more to how Riot styles things than about an issue in
nheko itself.

errors

Update dark and system themes to provide
colors for the hover states for title, subtitle, and timestamp.

Add room list hover title/subtitle color change support.

fixes #161

fixes #409

fixes #446

fixes #447