Update coach_dashboard decorator

[cewing]

The new version should determine if a ccx is active by using the course_id from the URL match.

If it builds a CCXLocator, then a ccx has been requested and the decorator should find the ccx and pass it in to the wrapped view.

If it builds a CourseLocator, then there is no active ccx and None should be passed to the views as the active ccx.

Views will be responsible for accepting a ccx or None, and if needed will raise appropriate errors or redirect appropriately if a ccx is required but not supplied by this wrapper.

[cewing]

@pdpinch: I am transcribing tasks for the ccx id switch into github ids.

[cewing]

This is completed, @pdpinch