Disallow free verified course modes
*Background:* The verification workflow assumes that all verified courses will have a price. Free verified course modes cause a 404 when the user attempts to enroll or upgrade.
This pull request adds a validation check to the `CourseMode` model to check that a price has been set if the mode is set to `validation` or `professional`.
*Testing:* Create a `CourseMode` instance in the django admin with mode `verified` and price 0.
Expected: fails with a validation error
Previous behaviour: accepted. Attempt to upgrade to verified course results in 404:
<img width="870" alt="screen shot 2016-01-29 at 13 58 47" src="https://cloud.githubusercontent.com/assets/793379/12669187/1c3097be-c691-11e5-92be-87d34e3d4a52.png">
Click 'Upgrade to Verified':
<img width="632" alt="screen shot 2016-01-29 at 13 59 35" src="https://cloud.githubusercontent.com/assets/793379/12669188/1c362256-c691-11e5-942d-13ae65067e10.png">
Doc on ecomm doesn't go to this level of detail. Removing documentation label, my assumption is that the UI indicates the required fields and that an error message appears if you do not supply all required values.
Second attempt merged
we lost track of this. It's been near the top of our backlog but hasn't been picked up. can we make sure one of our subteams looks at this OSPR in the next sprint?
Bump - any idea when your team might get a chance to take a look at this?