[WIP] Extracting Event and Entity related logic into Tickit\Component

TODO:
- [x] Fix the mocking for `AbstractEntityEventDispatcherTest`
- [x] Decide on a namespacing strategy for component specific events (will keep these in their respective components)
- [x] Refactor entity related events to `Tickit\Component\Entity\Event`
- [x] Extract all managers into `Tickit\Component\Entity\Manager`
- [x] Extract all repository classes
- [ ] Improve decoupling between `UserManager` and `FOSUserBundle`
- [ ] Fix the repository tests so that they are not dependent on bundles
- [ ] Move entities into `Tickit\Component\Entity`
- [x] Update Doctrine configuration so that entities are loaded from `Tickit\Component\Entity` with an alias prefix of `Tickit:` 

Coverage will decrease slightly on this PR, because the entity event dispatchers have been consolidated to a single abstract dispatcher class.