Merged class Drop into DropController

closes #112.

* Moved functions from Drop.java into DropController.java
* Deleted Drop.java
* Renamed DropTest.java to DropControllerTest.java
With #205 CryptoUtils are not a singleton anymore. If that PR would be merged first, this would not work anymore. Since this method has been moved into a new class, git would still mark this PR as mergeable. So watch out...