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
Update class diagram
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
Fixes #155 Handle unknown drop message types
Added test case to handle unknown drop messages

"Unknown" means types of drop message no one registered to listen for.
Removed ununsed imports
Merge pull request #209 from k-c13/class-diagram

Update class diagram
Merge pull request #211 from thechauffeur/got-drop-message-from-unknown-module

Handle drop message from unknown module