Mobile xBlock API

Mobile xBlock API  (18 days)ormsbee/iframe branch for LTI work  (4 days)exposes an endpoint for HTML content for xBlocksMissing: refactoring the code, probably unit testsUpdate CSS for the assessments that are required for Q4.  (8 days, high uncertainty)Possibly look at diffs in the Japanese repo.For all xblocks required for Q4.Mixin for Mobile-ready (2 days)Create a new xBlock Mixin class for mobile-ready xBlocksthe mixin will have one additional field: mobile_readyMark the CAPA assessments and HTML xBlocks as mobile ready.Action: Communication with OpenEdx developersFuture Note: update demo xblock to have mobile-rendering method and possibly have a mobile-preview mode in the xblock developer toolset.xModules bundle JS code, which can be over 1MB.  (4 days, med uncertainty)See if we can unbundle on the server-side. If not, see if we can cache the JS bundle on the client-side.Can we be more aggressive on caching?