Update class diagram
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
Changed bit constants to byte constants
Renamed SYMM_ALT_TRANSFORMATION to SYMM_GCM_TRANSFORMATION
Throw InvalidKeyException instead of catch
Added and improved logging for catched exceptions
Removed unneeded re-initializations of gcmCipher
Added Javadoc about possible null return values
Added file/stream based en-/decrypt methods w/ tests
Merge pull request #218 from thechauffeur/roeslpa-thechauffeur-fileStream
Removed generic parameter from DropMessage and replaced its data element's type with ModelObject.
Adapted unittests to Non-generic DropMessage object refactoring.