Can't delete container or element inside container

[drucelweisse]

closes #168

Added method to array of any AccessibilityView

wrap document method to use them

wrote some deletion tests

[drucelweisse]

1. Should we delete container if it becomes empty after element deletion?
2. Should we delete container with children or ungroup before deletion? (probably it just for ungroup function)

[drucelweisse]

And as well found bug where didSet property observer on VODesignDocument.controls doesn't know about A11yContainer children deletion. And undo doesn't work

[akaDuality]

1. I expect that container is important and shouldn't be deleted automatically
2. We should add ungrouping button firstly :D

I'm investigating undo function right now, probably will fix the bug