Segment and sort the home screen

[SyntaxBlitz]

Likely depends on #5.

The home screen should be segmented by the course the language is taught in. Courses taught in the user's locale should appear first (with English as the default). There's no need for a header on this top section, but subsequent sections (for different 'source' languages) should have a header explaining: "Courses in Spanish". With #2, all of these headers should just appear in the user's locale.

Other sorting (in order of priority, and open to discussion):

• Sort by progress: in-progress courses, followed by never-started courses, followed by completed courses
• Sort by recency: the more recently-used courses should show first. Right now I think we can only determine which course is most recently used rather than when each course was last used.
• Sort by course type: "complete" courses before "intro" courses (with German likely counting as an Intro course for now)
• Sort by popularity? Is this subjective, or is it based on live metrics? Right now we just use the sort on the LT website.