CMS: When a new program is created, create a CMS group to go with it

[pdpinch]

As a MicroMasters team member, I'd like to restrict editing of my program page to only members of my team.

Wagtail supports groups, but it's tedious and repetitive to set them up. We should create a group for each program, when the program is created. The appropriate permissions should look something like this:

This depends on the program page existing, as suggested by #686