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