Use a separate window for the Tile Collision Editor

Resolves shortcut conflicts for cut, copy, paste and delete.
Worked around an issue with static child widgets of child windows

Using static child widgets in child windows can cause a crash on exit
because there is a chance that they are still referenced after being
deleted.

In the last commit the Tile collision editor was changed to a child
window and the MapView has a static viewport widget by default. This is
flag is no longer used to avoid the above issue.
Manage the tool bar outside of the ToolManager

This simplifies the code and provides more flexibility. It's also safer
since ownership over the tool bar is more clearly defined this way.