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 
You know how much code you need to handle this `int[]` correctly? You even added a method to add an element to this "list" (which is not a list technically, I know). Why do you not just use a proper list without adding error-prone code? In Java you generally don't need to write something like
```
private int[] addElement(int[] array, int element) {
    array = Arrays.copyOf(array, array.length + 1);
   array[array.length - 1] = element;
   return array;
}
```
yourself. I know that you can't use the basic type `int` there but since you only use this internally you could make your life easier without doing this.