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.

This reverts commit 965e3b4c, reversing
changes made to 1a7d2a06.

I accidentally merged this before it was ready.  This was silly, so now I'm undoing it.  We'll need to revert the revert later.

update to show cohort name on create and cohort name on view all threads, added cohort dictionary to convert ids to names

- Create new cohorts.py file
- moved code there from models.py
- implemented necessary functions.

Next: testing :)

fix cohorts in create, and read, and update regular expressions to fix courses with periods not working in General commentable

following if it wasn't working before.