Incorrect capacity when dragging an item back and forth between connected fsortables

### Need
```gherkin
Given I have 2 connected fsortables
And the first one has size 5 and capacity 5
And the second one has size 3 and capacity 2
When I drag the item from the second fsortable to the first one
And then I drag it back to the second fsortable
And then I drag it back to the first fsortable
And then I drag it back to the second fsortable
And I drop it
Then the first fsortable should have capacity 5
And the second fsortable should have capacity 2
```

### Actual
The second fsortable will have capacity 3

### Prerequisites
- inspect the event flow in this case
- [line 252](https://github.com/NiGhTTraX/jquery-fsortable/blob/master/src/jquery-fsortable.js#L252)

### Solution
Fix how we handle items coming back to us after they were dragged to a connected sortable.

### TODO
- [x] fix updating capacities
- [x] write tests