Longitude and latitude in model for conceptdescription
Fixes and cleanups around user event lists:
 - rationalise some templates
 - get rid of redundent 'more' action for activity list
 - handle showing/disabling of 'More' button when no events are
   available
Merge additional changes by Thibault.
Add virtual unit content type
Abstract some boilerplate for caching future responses
Revise some terminology
Add (hidden) long/lat to concept form
Merge remote-tracking branch 'upstream/master' into guides