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
The treatment of a KeyError as opposed to a generic exception is nearly identical below, except there is some logging done the the former case.  Please consider having the one except block and just add the line to log the exception.