KAZOO-2934 allow html template
KAZOO-2934 use cache
KAZOO-2934 move content_type_to_extension to common module
Merge branch 'master' into KAZOO-2934

Conflicts:
	applications/crossbar/src/modules/cb_modules_util.erl
Merge pull request #575 from 2600hz/KAZOO-2934

KAZOO-2934 html template