it appears we are taking one too many round trips to do when pre-fetching children. This can be very expensive as the tree gets wider the deeper we go. For example, in courseware we want depth=2 (course, chapter, sequential). But looking at log output we were also getting verticals, which there can be a lot of. This should cut down on the total data we are grabbing from the DB.

if we're loading a course module with depth = 0, then we don't need to fetch/compute inherited metadata

- improve docstrings
- only pass in the state for a particular input and
not the whole dictionary
- refactor some common code
- minor syntax cleanup

Clean up some pylint errors

and add in a handler for ungraded responses via xqueue

the ModuleSystem.

- beginnings of new Matlab input type
- update progress after getting a response from xqueue

add a finally statement to be sure to turn back on event firing on writes in case an import throws an exception

Have to explicitly specify safe option on mongo insert, remove, update because the debug toolbar specifies a default of safe=False.

Always compute the metadata inheritance tree, even on a course module, so that when walking down the tree, we always get the right data

add an array of courses to not refresh the metadata cache on writes. This is needed for imports where we are doing bulk updates otherwise, the DB gets thrashed and the import takes too long, timing out the browser