Rc/2015 06 15

User api email update

There are now folders under static that have sass that should not be compiled
as a part of our asset pipeline,  they were getting pulled in because the wildcard
for `SASS_UPDATE_DIRS` was too broad.  This update makes it more specific for most
folders but leaves it broad for the common folder where the xmodule has its own sass
that needs compiling from a non-standard location.

Use a plain error page which don't require any rendering context

Improve social stats dumping functionality

simplify

Fixing various issues after birch rebase

 * Extracted common template parts in index.html and discussion_course into standalone template file
 * Improved discussion router test, so now it actually tests loading thread not in collection

Restored proper course discussion section in index.html to avoid including discussion js and css twice

Load thread if requested thread isn't loaded yet.

Cdodge/digest support

Updated problem builder hash to include feedback persistence changes