Putting `editregions_template_field = 'x'` onto a ModelAdmin instance
with an EditRegionInline allows dynamically refreshing regions & chunks
on form field change.

Merges branch `ajax_template_selector` into `master`.
Squashes commits:
57c5ce45bac99d573d2ba70800b3290a7cf12b82
6946bed28ee6145a915caf4b8f9648ea26d0a8b3
298813a1fb748a2f7c992244e18adcf0395850df
51ed6680d947a4ffa023a3cbd21fbd34cf1c7de4

Origin branch may still be at:
https://github.com/kezabelle/django-editregions/commits/ajax_template_selector