xblock lms integration for TIM

A few minor tweaks to make our TIM XBlock work in LMS, and load in Studio (though it cannot be edited just yet, even via XML)

Mostly small tweaks, but I'd also like you to take a look at the "DEFAULTS". I pulled them from the original ORA. Given we have those, we may want to drop one of our example XML rubrics for clarity, or move them into separate files?

@ormsbee @jrbl