(WIP) RTL

This PR sets up LMS and Studio to support RTL languages. Not every detail has been accounted for*, but every page should generally support layout from right to left. 

@talbs can you check the sass? 
@nedbat can you help with mako variables (and switching body classes) on the html templates - and review as you see necessary? 
@shnayder @sarina can you check from an LMS standpoint?
@cahrens can you review for Studio?

NB: This branch currently has come hardcoded values that need to be variable-ized before merging.

*Expanding arrows have not been rotated around, prev/next arrows have not been switched, and other small details I may not know need fixing may exist.
Yes, to make the layouts more consistent and reduce the layout changes i needed to make, i abstracted out the layout so we would only need to do the switch in one place. i used the class rather than the placeholder because the sass was not respecting the placeholder. i'll make a note to follow up and see if the new sass will respect it in a separate PR.