REGISTRAR,RPC: support for re-sending notifications

- Added method to to re-send notification related to the application.
  Perun admin can send any notification, others are limited to
  actual application state.
- Added same method to RPC, added getApplicationById() to ApiCaller.
- Set AppState to application on creation.
GUI: support for re-sending notifications

- VO/group admin can now re-send notification on application detail page.
  Selection of mailType is filtered based on actual application state.
  Perun admin can send any notification.
  USER_INVITE notification can't be sent this way.
REGISTRAR: allow RPC to call getApplicationById()
REGISTRAR: Throw exception if mail notification can be re-sent
Merge pull request #465 from zlamalp/notifs

REGISTRAR, GUI: support for re-sending notifications