capa problem answers may have static urls - needs replace_urls

Don't display 'None points' on problem rendering

Fix all of askbots style

Kimth/sjsu

URL based course lists

Feature/victor/strip metadata

* if there is a policy.json in the course dir, read it
* file format is a dict with keys {category}/{url_name}, and values metadata dictionaries
* apply the policy, overwriting keys that are in the xml
* then do metadata inheritance, inheriting any overwritten keys.

* also a management cmd to generate a policy.json from a course dir.

Feature/victor/start dates

Rename acquire_lock to select_for_update, add docstring

- don't call has_access directly from template, pass a staff_access variable instead