django-compress doesn't work well with cache. If horizon is
deployed in a containarized environment with pre-built static
in images, django-compress tries to load old templates from cache.
This patch introduces following changes:
* update_angular_template_hash uses the correct Django cache backend now
* fixed cache cleanup for memcached backend
* added clean_angular_template_cache management command to clean cache
manually without executing heavy 'compress' command.
Closes-Bug: #1874657
Change-Id: If1fd61fa2e4b36e22797b0f54ac067a2a937f369
