Copy brick issue

When copying a brick from context dialog the new brick is inserted at the position of the old one. The previous implementation inserted the copied brick at the end of the list. When the brick list exceeded the screen size the copied brick was not inserted until scrolled to the end of the brick list. Therefore it was possible to select ```Copy Brick``` again before the first one was inserted leading to the crash.

Fixes #617 

https://jenkins.catrob.at/job/Catroid-Multi-Job-Custom-Branch/334/