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
There isn't really a more useful message for the user in this context. Re-raising and logging the error might make more sense.