Rework Manage Bookmark dialog

- Make it single account
- Use a Treeview
- Move it to advanced sub menu

Manage Bookmarks should serve in the future as dialog for advanced users.
During normal usage of Gajim there should be no need anymore to access this dialog.
3 jobs for master in 45 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Test
failed #12676
run-appdata

00:00:03

failed #12675
run-tests

00:00:45

 
  Build
skipped #12677
run-build
 
Name Stage Failure
failed
run-tests Test
    Not uninstalling astroid at /home/gitlab-runner/.local/lib/python3.6/site-packages, outside environment /home/gitlab-runner/builds/c0eaa480/0/gajim/gajim/civenv
Can't uninstall 'astroid'. No files were found to uninstall.
Found existing installation: pylint 2.1.1
Not uninstalling pylint at /home/gitlab-runner/.local/lib/python3.6/site-packages, outside environment /home/gitlab-runner/builds/c0eaa480/0/gajim/gajim/civenv
Can't uninstall 'pylint'. No files were found to uninstall.
Successfully installed astroid-2.2.5 pylint-2.3.1
$ mypy gajim
gajim/common/modules/bookmarks.py:228: error: Return value expected
ERROR: Job failed: exit status 1
failed
run-appdata Test
Running with gitlab-runner 12.0.1 (0e5417a3)
on asterix_ci1 c0eaa480
Using Shell executor...
Running on asterix-ci1...
Fetching changes...
error: could not lock config file /home/gitlab-runner/builds/c0eaa480/0/gajim/gajim.tmp/git-template/config: File exists
ERROR: Job failed: exit status 1