Feature/sections identifier

Contains the following:
1. Check for resource_link_id match with current session
2. URL changes for the above
3. Check section's course id for match with current session
4. Error handling for 1 and 3 above
 Note: unit tests (new and fixes for ones broken by above changes) to follow in another pull request
Retrieving the section from the SDK could potentially raise an exception.  We may want to wrap this call in a separate try/catch so we can log and re-raise or display a more appropriate message than the Context error that would otherwise be displayed below.