Merged class Drop into DropController

closes #112.

* Moved functions from Drop.java into DropController.java
* Deleted Drop.java
* Renamed DropTest.java to DropControllerTest.java
Unlike ```Drop``` this class doesn't have a generic statement here. Am I right that this is not needed anymore because the generic definitions have been moved directly to the migrated ```Drop``` methods?
If so, does a caller has to do something specific when calling these methods?