This is the bug that sbar found when pulling a sub-hierarchy out of a
larger hierarchy: child indices not getting updated correctly for later
siblings and any niece objects.
The hierarchy-specific tests from the transform tests have been moved
into the ecs tests and the transform tests renamed appropriately. As
part of the process, hierarchies can now have a null type (ie, no
additional components maintained by the hierarchy). This should make
sorting out the issues highlighted by sbar a bit easier.
While the libraries are probably getting a little out of hand, the
separation into its own directory is probably a good thing as an ECS
should not be tied to scenes. This should make the ECS more generally
useful.
