Show notifications in notification bar

Fixes #28.
3 jobs for 28-notifications in 3 minutes and 22 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Test
passed #6041
pycodestyle

00:01:20

failed #6042
pylint

00:02:02

manual #6043
allowed to fail manual
pytest
 
Name Stage Failure
failed
pylint Test
Unable to init server: Could not connect: Connection refused
Unable to init server: Could not connect: Connection refused
************* Module briar-gtk.briar_gtk.window
briar-gtk/briar_gtk/window.py:77:4: R0201: Method could be a function (no-self-use)

-----------------------------------
Your code has been rated at 9.99/10

ERROR: Job failed: exit code 1