Stable 7 port

:construction: 

Port to the new framework features in owncloud 7 (database, logger, controllers). Depends on PHP 5.4

Don't merge yet, keeping this open just for reference and to track the process

Additional todos:
* [x] Convert array() to [] to get rid of visual noise
* [x] Make Entity Attributes private like they should be and implement JSONSerializable interface to convert them into an array that json_encode can read

Some PHP 5.4 features that can and will be used :smile: (finally):
* Traits (Controller\\JSONHttpError)
* Shorthand array syntax: [] instead of array()
* $this in closures
* JSONSerializable interface which allows you to create your own method that is executed when you do json_encode($obj)
* Function dereferencing (e.g. $obj->getArray()[0])
* Class member access on instantiation, e.g. (new Foo)->bar().

As for PHP 5.5: The only interesting new feature would be the finally keyword to improve error handling but I dont think we have a usecase in the code so 5.5 transition is not as important as 5.4 and can be done sometime later if support is good enough