Changed user enrolment to set default section

If section ends in "00" (e.g. D100, E100, G300) or if only 1 section in the course (i.e. no section tutorials) then enrol teacher to that section.
Merge remote-tracking branch 'upstream/sfu-develop' into course-form-plugin
Hide Sandbox course option if one already exists for the user

Added JSON call to get sandbox info if exists.
Fixed typo in variable name
Minor text edits on form and confirmation page
Changed title of form to match Canvas button and the original course form
Merge pull request #22 from ronvs/course-form-plugin

Course form plugin
CANVAS-159 create high-resolution assets for the canvas theme

I don't have source files for the backgrounds, so this just covers
the logos for now. That's probably enough.

add 2x version of sfu-canvas-logo.png

add 2x version of sfu-logo.png

use 2x versions of images
Merge pull request #23 from grahamb/canvas159-retina

CANVAS-159 create high-resolution assets for the canvas theme