Issue #2936365 by quietone, mikelutz, heddn, larowlan, masipila, effulgentsia, maxocub, Gábor Hojtsy, webchick, phenaproxima, jhodgdon, catch: Migrate UI - allow modules to declare the state of their migrations

Issue #2711099 by heddn, Jo Fitzgerald, edysmp, edgewl2, alexpott, Charlotte17, mikeryan, masipila, quietone, maxocub, phenaproxima: Categorize migrations according to their type

Issue #2917883 by quietone, TR, Jo Fitzgerald, masipila, phenaproxima: Rename 'migration_templates' directories in core modules to 'migrations'