CLC-3528 - Re-name and change Canvas 'Start a New Course' buttons to link to Course Provisioning tool

https://jira.ets.berkeley.edu/jira/browse/CLC-3528

* Adds new public API end point - /api/academics/canvas/external_tools, serving the names and IDs for each configured LTI application in Canvas.
* Updates Canvas Javascript customizations so that User Dashboard and Course index page are scanned for presence of 'Start a New Course' button. Once found the button is replaced with the custom button, and the scanning loop is stopped.
* Hides 'Start a New Course' button within Canvas to ensure it is not seen, but can be manually re-enabled as a work around.