added new method getKeyIdentifier() in class Identity
Class Contact:
* new field contactOwnerKeyId
* new protected constructor with parameter contactOwnerKeyId
* new getter for contactOwnerKeyId
* new setter for contactOwner
* modified constructor with parameter contactOwner
new class ContactTypeAdapter
added test for Contact de-/serialization
Merge pull request #171 from f-porter/Issue71-Contact-Key-Serialization

Issue71 contact key serialization
Added HMAC and GCM en- and decryption
added encryption functions with nonce parameter
ctr mode test vectors are working
gcm mode test vectors are working
removed unused imports
added handling of nonce=null and counter.length=0
finally added second nonce=null handling
added comments for code understanding
Merge pull request #146 from roeslpa/apply_test_vectors

GCM and CTR mode with 96 bit nonce
Fix #111 Drop::sendAndForget can return a false value
Move DropResult and DropResultPair to a new class
Update DropMessage<T> to DropMessage<? extends ModelObject>
in class SyncedSettings: * added new field contacts * added getter and setter for field contacts * added new field initialization in class constructor
in class Identities: * changed collection type from Set to Map in order to enable retrieving identity by key identifier * adapted change of collection type in add() method * added getter getIdentityByKeyIdentifier()
in Class ContactsTypeAdapter: * use now proper ContactTypeAdapter in write() and read() methods