Initial work on #2126 to default the `static` templatetag to use the `BUILD_HASH` get url parameter.
Merge pull request #2194 from cpauya/feature/2126-Make-reloading-the-static-files-based-on-BUILD_ID-the-default-behavior

Include the `BULD_HASH` in the `static` templatetag by default.
Don't stick build id on end of base STATIC_URL used in khan-exercises.
add setting for turning off motivational features
mark some HTML elements as motivational features that can potentially be disabled
add ab_testing.css
hide knowledge map icons when we toggle off motivational features
set the real_password for student mixins
indent html by 4 spaces
check local_settings for the value of TURN_OFF_MOTIVATIONAL_FEATURES
add TODO-BLOCKER to move ab_testing.css to future ab_testing app
add assert to make sure we have Nalanda package activated
Merge pull request #2200 from aronasorman/2167

Don't show some UI elements depending on the value of TURN_OFF_MOTIVATIONAL_FEATURES