Should be possible to make repositories 'read only'

[rtholmes]

While this should ultimately be controlled by 340s schedule code, for now at least make it possible to stop students from committing to a repo.

The easiest way, although unsatisfying, would be to take the student team off of the repository on GitHub. Essentially this puts the repo in an 'unreleased' state. Then we can 'release' it later to put the teams back on so they have write access again. Note: this does mean that they won't be able to look at their repo in the web interface either. The nice thing about this is we already have 'release' code, although we don't yet have 'unrelease' code.

An alternative is to just toggle the team's permissions from write to read. This would be with the following API: https://developer.github.com/v3/teams/#add-or-update-team-project

Since this would require new UI (probably just in the 'provision and release repositories' pane, it might be nice to update 'provisioned repositories' and 'released repositories' as listboxes as well so there isn't infinite scrolling on these pages anymore.