modification of @jrbl's version to handle a dict with value None

Make django use_tz

This reverts commit 2df3fe93.

Conflicts:
	common/static/coffee/src/discussion/utils.coffee

This reverts commit acfd0d9f, reversing
changes made to e4194c99.

remove discussion caching for now. It might be overkill and I need to figure out how to serialize out the resultset into the cache as writing modules into the cache causes a pickle error

optimize forum page rendering as we don't pre-compute the link urls to inline discussions. We can use jump_to urls and then figure out the link path if/when end-user clicks on it. This saves a lot of unnecessary round trips to the DB as path computation is expensive, especially when it being done for every discussion module in a course in a loop.

This reverts commit e4819a1b, reversing
changes made to b6ec41ca.

Now that we're ready to test again, need to revert the revert to put the filtering UI back in.

This reverts commit 66889b87, reversing
changes made to 0dd9c24e.

This was merged too early--it's still missing the filtering and display-your-cohort changes.
Will need to revert this revert later.

make LMS forum subsystem more robust in case of orphaned discussion modules. Given our draft/non-draft duality, we don't currently have a means to always do proper housekeeping at this point in time. However, we have to stop the LMS Forums from blowing up when encoutering one of these.

only cache discussion forum info for 5 minutes before flushing. This is needed for Studio backed courses that can add new discussion items at any point in time. Also we need to also set metadata fields (which are basically the same as what gets passed in the XML) as the forums expect those values as metadata

change over the 'get all discussion models' to use get_items() which is better supported in Mongo-backed stores