Add support for gnome-shell polkit agent.

The gnome-shell desktop does not uses a separate process as others do.
It uses an agent within its own process so we need to check for
gnome-shell and then assume that its polkit is working.
add version command
check for uid == 0
pep8 cleanup
add bitmask-root notes to checklist
update manpages
Merge remote-tracking branch 'refs/remotes/kali/feature/bitmask-root-versioning' into develop
style fixes
remove BOM char from relnotes.txt. Closes: #5745
Merge remote-tracking branch 'refs/remotes/ivan/bug/support-gnome-shell-polkit' into develop
Merge remote-tracking branch 'refs/remotes/kali/fix-weird-chars-in-relnotes' into develop
Grep for gnome-shell as it were a polkit agent.

The $DESKTOP_SESSION is not reliable since is set to 'default' in any
case that you choose as your default desktop environment.

Also, after some tests, I've seen that the `gnome-shell` process is not
launched in the fallback mode, so we use it as a condition for the
polkit agent present.
Reorder logging helpers and handlers.
check if resolvconf is missing in system
change elements naming
Merge remote-tracking branch 'refs/remotes/ivan/bug/improve-gnome-shell-detection' into develop
Merge remote-tracking branch 'refs/remotes/ivan/feature/reorder-logger-tools' into develop
Merge remote-tracking branch 'refs/remotes/kali/feature/init-check-for-resolvconf' into develop
Merge remote-tracking branch 'refs/remotes/kali/bug/ui-elements-rework' into develop
Move quit callback to mainwindow.