Add move into the TreeModel interface

[OndrejSpanel]

Implemented a move in the tree model. While move can be replaced with delete / insert, this has some serious drawbacks:

• it is hard to validate the move (and to prevent it when the move should not be done)
• it is hard to handle failures (second operation can fail, while the first has already completed)

This pull request adds move into the TreeModel interface, it implements move in the internal tree model and provides a demo implementation for both internal and external model demos (using Cut / Paste interface).

[OndrejSpanel]

Closing, PR contains unrelated commits container in other PRs.