Made DropSerializer test working.

Forgot how to use embedded classes...
remove unneeded imports
changed sourceCompatibility to 1.7
Update class diagram
Added en- and decryption
Added test for en- and decryption
removed new byte[], use byteArrayOut/InputStream
Merge pull request #50 from jan-schreib/build.gradle

changed sourceCompatibility to 1.7
closes #2
Merge pull request #51 from roeslpa/basicSymmetricEncryption

Basic symmetric encryption
Added hybrid encryption and decryption method to CryptoUtils (encryptMessage and decryptMessage)
Merge pull request #52 from L-Henke/hybridEnc

Added hybrid encryption and decryption method to CryptoUtils
Merge pull request #47 from jan-schreib/dropserializer-test-fix

Made DropSerializer test working.
added .travis.yml

closes #13
updated travis file