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]

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.

- 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.

The scrollbar will stay in the same position if new messages
are added to the bottom of the timeline.

Fixes #95