Add utility functions for working with Django Migrations.
Review Request #10558 — Created May 21, 2019 and submitted
This introduces some utility functions that help with several steps in
the Django migrations process. These include functions for retrieving
all applied migrations organized by app label, recording batches of
applied migrations, filtering migration targets by app labels, and
actually applying migrations.
These will be used by an upcoming change that coordinates the evolution
and migration processes in the evolver.
Unit tests pass for Django 1.6 and 1.11.