Add new classes DropResultContact and DropResult
Fixed #111: Drop::sendAndForget can return a false value
Update documentation
Change spaces to tabs
Use function addElement
Delete not used code
Update documentation
Remove not needed function
Update documentation
Add public to function (cosmetic)
Update code style
Update code style
Update constructor
Merge branch 'master' into k-c13-drop-send-v2

Conflicts:
	src/main/java/de/qabel/core/drop/DropController.java

- Kept improved logging
- Adapted to change in master to use only one key from
Contact.getSignKeyPairs()
- Kept TODO mark on improving that
Merge pull request #217 from k-c13/drop-send-v2

Fixed #111: Drop::sendAndForget can return a false value