EZP-23142: API Signals are not transaction safe

Short: Signals must be emitted when commit is performed as there is no way to perform rollbacks on signals. This also removes the needs for the commit events as signals becomes inherintly commit safe.

Todo:
- [x] Implement in SignalSlot Repository
- [x] Adjust configuration
- [x] Adopt Solr handler Slots and remove use of commit event system
- [x] Deprecate commitEvent system
- [x] Rebase with issue number: https://jira.ez.no/browse/EZP-23142
- [x] Adjust if travis complains