(+) naive key exchange over NFC

(+) Some interfaces for key storage, encryption, authentication
Merge branch 'master' of https://github.com/glukas/Social

Conflicts:

Social/src/ch/ethz/inf/vs/android/glukas/project4/protocol/Protocol.java
Merge branch 'master' of https://github.com/glukas/Social

Conflicts:

Social/src/ch/ethz/inf/vs/android/glukas/project4/protocol/Protocol.java