Save improvements

Save active layer
Recursively save children
Renamed CanCopy to CanSave
Scene manager clean up.
Fixed allocation bug

When we allocate new entities from a big list of entity data, only
return the entities that have no parent. Entities with parents are
included implicitly due to the fact that they have a parent.
Log message for entity add / remove
Added redraw request message

Needed to add a redraw request message to handle the case where events
get triggered on a non-UI thread.
Missed this for the last check-in
Half assed attempt at file open

This isn't thread safe right now.

Thing I should move the save / open work into the jobs themselves and
move the jobs into the TileToolApp assembly.

Job final step on open would be to create command to put everything into
the scene, but don't allow it to be undone.