add triggr timer dbus method.

Summary:
We think, that NotificationManager get all the Notifications we want to
see, so we need to debug, why he does not send the notifications out.
Maybe the timer is disabled or we have a strange intervall. Add a method
to trigger the notifications by hand, this way we can try, if this the
problem we should investigate further.

Reviewers: mollekopf

Maniphest Tasks: T1321

Differential Revision: https://git.kolab.org/D202