fixes #141

- Fix a memory leak where a layout was created without being used.
- Fix uninitialized value.

fixes #25

fixes #154

Try sending a message when all the sent messages have been received
through /sync.

fixes #115

fixes #24

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]