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