testMaker Code

Remove some old commented-out code.

In all cases that we update structures, update all blocks that contain the modified object.

Make TestStructure::getTrackedContainingTests support subtest mode too.

On deletion pages, display warning about disabling whenever applicable.

Add infrastructure to better detect whether structure needs to be tracked.

For structure changes, we now consult all tests that contain the object in
question and update their structures if required.

Also, a couple of new doc comments.

Add more support for read-only mode.

Clean up and clarify modification warnings on lots of editor pages.

Properly handle and display disabled item answers.

Introduce read-only mode for BlockPage descendants to handle disabled objects.

Fix typo in disabling support for item answers.