Wikivoyage migration/Extensions

Task Assignments

 * Create git repos - Sam
 * Architecture Reviews
 * Mlitn: MapSources, GeoCrumbs, Calendar, CustomData, GeoMath, Insider, RelatedArticles, RelatedSites, TocTree, CreditsSource
 * Security Reviews - Chris
 * Install in Labs?
 * Test with 1.21
 * Deploy to Production