[WIP] Refactor event system

Hey, 

I refactored the event system a little bit. Now you can configure which listeners should be triggerd and which not. 
So if you have some issues with upload a file/image, like #8. You can disable the event listener and upload the file by hand.

Feedback, please!

### Todo ###
 - [ ] Tests
 - [ ] Test it in a real application
 - [ ] Make it workable with MongoDBODM