Execution of server side tests is broken by media comp support

[s-edwards]

The media comp library added to support image processing works with in-browser execution, but does not work on the server-side python installation, effectively breaking server-side checking of python code. We need an effective way to use Jython to perform the server side checks (should be fairly easy). We may also want to investigate whether we should provide server-side access to either Jython or native Python for testing assignment submissions (but how would we choose, or would we leave it up to the person creating the assignment?).

[allevato]

The Environment model represents the beginnings of how I was trying to design this. The idea was that an Environment was a representation of the runtime that should be used to execute the code, by providing minor code transformations (basically being able to prepend a "prelude" to the code before executing; this was to support the implicit media comp import), and later to support different ways of running the code server-side (hadn't gotten that far yet).

Environments could be set on a per-repository basis (for the scratchpad and examples), on a per-assignment basis (repos created from that assignment would automatically inherit the assignment's environment), and on a per-course basis (assignments would automatically inherit the course environment). So an instructor could choose "Jython + Media Comp" or "Python 3" as the environment for their course and it would just percolate down to everything else automatically.

So, the basic ideas are already in place, but the details of the implementation need to be fleshed out a lot more.