43971539 machine friendly note types

Two commits here to convert note types from human readable names ('Language of Materials') into machine readable codes ('langmaterial')

I've split this into two commits: one deals with the backend and UI changes to get the i18n translations for these codes set up.  The other deals with the changes I made to the migrations YML to work with the codes.  @lcdhoffman: Could you check that I got those right?  Hopefully I got them all.