Remove items from the shopping cart if they are for a course whose course enrollment window has closed

changed the url name to verify_cart and change the color of the message in the shopping cart
Added IMG tag instead of css background property for important visual indicator.
TNL-892
Merge pull request #6114 from edx/waheed/tnl892-fix-css-background-image-for-important-visual-indicator

Added IMG tag instead of css background property for important visual indicator.
Merge pull request #6124 from edx/muhhshoaib/WL-164

Unpurchased items in the shoppingcart should be removed if the enrollment period has closed
Load OVA JS with requireJS in LMS.
Merge pull request #5829 from edx/jmclaus/load_ova_js_from_templates_with_requirejs

In LMS, load OVA JS only in four OVA templates with requireJS. [TNL-693-outdated]
Make a generic django field for storing OpaqueKey classes
Extract common base functionality for storing xblock fields in the relation db
Move lms.lib.xblock into lms.djangoapps.lms_xblock in preparation add database backed configuration to it
Add a configuration model for managing XBlockAsides
Teach LMS how to render XBlockAsides

[PLAT-217]
Disable XBlockAsides in Studio
Make ErrorDescriptor more resistent to errors