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
I think we may want to have the same pattern for urls where the resource_link_id is the leftmost identifier.  I can see a future revision for this and some other similar urls where we will end up removing the sis_section_id and section_name from the url, so keeping the resource_link_id on the left would keep things consistent with top-level urls even if we shorten them.