Remove/replace usage of adminsortable2

[jmurty]

Per 4e64298 we are using the third-party library adminsortable2 in a very limited way in GLAMkit, per the comment below it's not working reliably even for this limited use. We should either fix it, replace it, or just remove it altogether.

django-icekit/glamkit_collections/contrib/work_creator/admin.py

Lines 76 to 82 in 4e64298

	class WorkImageInline(
	# Some super-weirdness means that this inline doesn't appear on
	# docker-cloud staging if SortableInlineAdminMixin is enabled.
	# Giving up for now. TODO: reinstate, or choose a different sorting ui lib
	# SortableInlineAdminMixin,
	admin.TabularInline, ThumbnailAdminMixin
	):