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.

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

fixes #60

Incompatible Qt version 5.5.1

[ci skip]

Fixes #95

Signed-off-by: Vitaly Zaitsev <vitaly@easycoding.org>

Signed-off-by: Vitaly Zaitsev <vitaly@easycoding.org>

Bug introduced on the last commit