Add option to disable notification at startup

[AndreaOrru]

Added a notify_startup option to the configuration file (defaults to True).

[eonpatapon]

This startup notification is for detecting if some service provides org.freedesktop.Notification.

Is it disturbing for you?

[grawity]

This startup notification is for detecting if some service provides org.freedesktop.Notification.

Hmm, that could be done quietly using GetNameOwner() instead.

(If you want to check whether there's an activatable service that provides o.f.Notifications, there are ListActivatableNames() or StartServiceByName(), but it's probably not a good idea to rely on auto-activation for such "multiple provider" names in the first place.)

[eonpatapon]

@grawity I will try to use GetNameOwner() instead then

[AndreaOrru]

This startup notification is for detecting if some service provides org.freedesktop.Notification.

Is it disturbing for you?

Not massively, but I would prefer not to have it :)
Feel free to close this PR if the other one addresses the problem.

Thank you!

[eonpatapon]

Thanks, other PR is merged