Type safety check

Added check in spline entity that is create data is of the correct type.
Work in progress Z ordering

Checking in so that I can work on another idea. This isn't finished,
working or even fully thought out yet.
Make collision take into account Z order.
Warning cleanup.
Deleted worklog

Using Git commit history as a worklog.
Added delete selection

- Hooked up delete selection to Delete key.
- Added command ID for delete selection.
- Handled delete selection in editor module.
Z order fixup on delete

Re-normalize the Z order on entity delete.
First real pass at Z order

Got z order working. Each time a group of entities are added to the
scene, they create a new Z-order.

Can move forward in back in Z-order.
Added parent child support for z-order

Moved the child add to scene operations out of the entity class and into
the scene manager.
Move Z ordering work.

Improved way Z ordering is handled so that parent child edge cases work
better.
Remove issue fixed

- If we can't find an object during a remove, continue on rather than
returning.
- Removed some code from add / remove action that is no longer needed
now that the scene manager will will add / remove entity its children.
Update TODO
Remove all Z order code.

Need to actually think this through rather than just try a bunch of
random stuff and watch it not work.