Automatically dismiss unread notifications when the window regains
focus.

fixes #111
fixes #68

fixes #134

The color scheme of nheko obeys the default color theme of Qt
(i.e. the system theme). It uses a Qt stylesheet to accomplish this,
which means replacing the color theme with a custom theme would only
be a matter of writing a new style sheet and loading it into the app.

[ci skip]

Fixes #64

This also fixes the transmission of mis-typed commands as messages,
fixes inability to send messages that start with a command, and does
some initial work towards automatically resizing the input field to fit
the input message.

fixes #116

The first message of the timeline would have an avatar and
the rest of the messages would use the previous to be configured
(whether or not should have an avatar).

fixes #63

- Ghetto disambiguation for the quick switcher
- Fix the Ctrl+K shortcut
- Fix keyboard focus when the quick switcher is closed

fixes #114

- Fixes high cpu issues caused by the serialization of the whole
  in-memory state.
- Display name changes are now visible in the timeline.