Gaphas: While re-sizing a child state size extends in opposite direction if mouse on boundary of parent state

If child states are re-sized and the mouse moves on the parent boundaries the child extends in the opposite direction. I talked to @sebastian-brunner and he also thinks that is buggy behavior.

Procedure:
- create a new state machine
- add a new state
- re-size the new child state till you reach the boundary (like on the right side) of the parent (so the child state is extending to the left)

I could estimate that the shrinking after moving with clicked mouse to the left again is an appropriate behavior but the extending only easily can be embarrassing if only accidentally touching the parent boundary. The shrinking or no extending of the state both could be a solution to the current behavior. Maybe we discuss it.

Finally this issue needs a representation (test) in issue #175 to preserve gaphas functionality and as reliability to the user.

Originally created by @Rbelder at 2017-02-24 17:19:43+00:00 (moved from RMC internal repository)

Reproduce the resizing procedure in the graphical editor by creating a state machine, adding a child state, and dragging it to the parent boundary. Read issue #175 for the requested regression-test representation and compare the shrinking and opposite-direction extension behavior. Done means the boundary interaction no longer causes unintended extension and the behavior is covered by a test.

Written by the indexing model from the issue text.