Extended coach reports, v1 (based on coach reports for IDOC training session)

I've refactored the code from the IDOC coach reports training session such that we can merge it into develop directly, with no dependencies on other IDOC code (yes this was a lot of work!!).

We have the following new pages, with lots of supporting code:
* A landing page for coach reports
* A scatter plot
* A timeline view
* A report on individual students, accessible both to coaches and to the students themselves.

Some common code changes and refactoring to accommodate the new coachreports app.  This is a big change!  Please take care.

Note that unrelated changes made in the same branch (csrf stuff, better UI experience for adding new users, etc) do not appear here, and will be added as a separate (small) branch/pull request.

Note also that the current code uses Google Visualization, which is unavailable offline.  Changes to make these coach reports available offline, and other TODO/feature requests, can be found at issue #137