Add buffered data classes
Add identity id
Update function name
Add new test function testing check function
Change AcknowledgeID::model_object from string to class<T>

Removed not used file
Add new classes DropResultContact and DropResult
Fixed #111: Drop::sendAndForget can return a false value
Merge branch 'drop-send-v2' into acknowledge-v2
Merge branch 'buffered-data' into acknowledge-v2
Add empty Drop class for sending acknowledge messageexit
Add ErrorObject in Drop as descriped in https://github.com/Qabel/qabel-doc/wiki/Qabel-Client-Drop#special-messages
Add function to create easily a filled drop message
Add function to create an acknowledge id
Add version number to Module
Add functionality to handle Drop message (acknowledge and error object)
Update test for Drop message (acknowledge and error object)
Add ErrorObject
Add acknowledge received to drop callback classes