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
new class SyncedSettingsTypeAdapter
in class Identity: * added annotation SerializedName("keys") to field primaryKeyPair
Merge pull request #159 from k-c13/drop-send

Fixed #111 - Drop.sendAndForget can return a false value
Fixed #165 Wrong (or naive) documentation of Drop.send()
Merge pull request #170 from k-c13/drop-documentation

Fixed #165 wrong (or naive) documentation of Drop.send()
Revert "Fixed #165 Wrong (or naive) documentation of Drop.send()"
Merge pull request #183 from Qabel/revert-170-drop-documentation

Revert "Fixed #165 Wrong (or naive) documentation of Drop.send()"
Revert "Fix #111 Drop::sendAndForget can return a false value"
Merge pull request #184 from Qabel/revert-159-drop-send

Revert "Fix #111 Drop::sendAndForget can return a false value"
In class SyncedSettings:
* added field contacts
* added setter and getter for field contacts
* added initialization of contacts to 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()
* added javadoc for new and modified methods
new class SyncedSettingsTypeAdapter
In class ConfigSerializationTest:
* split tests for SyncedSettings and LocalSettings
* changed test for SyncedSettings to use new SyncedSettingsTypeAdapter
* changed URLs in contactTest to match the DropURL format