Add primitive verification api for executing code

This is part of #140 

current status and working assumptions
* NOTE: You must do a database migration before running this on a pre-existing system.
* /verification/<pk> is a new api that creates a verification
* There is no distributed task queue for handling verifications.
* Verifications are not sandboxed.
* This runs jobs on the same server as the webapp.
* Article has a verification code archive that can only be edited via the admin
* Verification is a new table where information about verification jobs are stored, 
* An admin user will have to take materials provided by regular users and verify that contents follow the conventions of having `main` and so on. example https://github.com/researchcompendia/rc460example