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
Just curious: if you redirect the user back to the top-level page in case of the context error will they actually see the error message telling them they need to relaunch the app?  If they can't see the error on the screen, then they might not realize why they've been redirected.