Modified: CryptoUtils is not a singleton anymore

This avoids multi threading issues.
Key related methods were moved to the QblKeyFactory singleton class.
Changed QKF methods using CryptoUtils to synchronized
Merge pull request #205 from L-Henke/nonSingletonCryptoUtils

Modified: CryptoUtils is not a singleton anymore
Utilize KeyGenerator to create AES keys

as proposed in #53:

utilize the Java KeyGenerator to create AES keys instead of using raw
byte arrays filled by SecureRandom.
Merge pull request #186 from L-Henke/aesKeyGenerator

SecretKey for AES keys instead of raw byte arrays
Merged class Drop into DropController

closes #112.

* Moved functions from Drop.java into DropController.java
* Deleted Drop.java
* Renamed DropTest.java to DropControllerTest.java
Merge pull request #204 from jan-schreib/drop_refactoring

Merged class Drop into DropController