reordered email settings checkbox to impact styling for icon and cleaned up header navigation for discusisons

basic shell for home page exists, along with start of color cleanup for the rest of _discussion.scss

cleaned up variables styling to sync up closer to studio, incorporated fontawesome icons into discusison home with basic positioning

cleaned up font-awesome integration to work with new mako file .scss compiling, added in initial icon references

addition of font-awesome to LMS sass vendor assets, in additio nto light organization for applicaiton.scss to match studio sass breakdown.

Two endpoints are intended to be used by AJAX calls from the web UI with an
authenticated user. When enabled, the value of the preference is an encryption
of the username, to be used as a token for one-click unsubscribe links. The
third endpoint is the target of unsubscribe links, which displays a page with
an appropriate message to the user.