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

Add new classes DropResultContact and DropResult 
Fixed #111: Drop::sendAndForget can return a false value

Close #195 
I do not use this list only internal. As you see 
public int[] getErrorCode() 
give you the list. So you can check what is the problem.

If you want to know why your message was not able to send when the other side have more than one drop server so you have to know why. And for that is that list.

If you want an other solution as that tell me how you want it.