Ora2 aggregated data download button and management command

This is a pull request for an Ora2 aggregated data download button.  It is located in the Data Download section of the Instructor tab in edX.  It runs a raw SQL query located in instructor.utils (formerly located here https://gist.github.com/wedaly/f17ba1d2fffae65545c8) against the database.  This request also includes an associated management command, which performs the same query against the database, and can save the output file to an optionally specified directory or print it to stdout.

It would be nice if you guys could take a look at it and make suggestions before I attempt the upstream PR.  @jrbl @stvstnfrd @jbau @kluo 
I'd prefer if you used argparse or optparse for command-line parsing. If you do, you can specify the metasyntactic variables, the help lines, and the defaults for you arguments and options, which means in the help output you'll get nicely-formatted descriptions of the args and opts, without having to describe them in paragraph form.

I forget exactly, you'll want to look at other examples, but it's either the docstring of Command or of handle() that gets used as the usage summary. Whichever it is should be written to be a nice usage summary. If you can write something nice that also conforms to pydoc convention - one line pithy imperative summary followed by a blank line followed by amplification - that would be even better.