Renamed script to sync local mbox directory with remote from `mail-check`
to `sync-mail`. Changed necessary integrations accordingly (neomutt and
system service).
Detect X autostart a bit better with a separate service. The service
relies on a shell script which searches for a socket which X creates on
startup and only finishes when it finds the socket succesfully.
This makes services which need X to start successfully a bit more
robust, and while it can still break if X takes too long, it should be
more stable now.
Finally, services can restart more quickly when ended since they don't
require the 2+ `RestartSec` option to be present anymore to successfully
start.
