fixes #6519 - updating associations UI

Added associations to the UI:
+ subscriptions to content hosts and activation keys
+ activation keys to content hosts

I wonder if `$scope.statusReason += reason.attributes.name + ': ' + reason.message + '\n';` would be easier to read  if there are multiple reasons.  I'm not a big fan of doing this formatting here but I suppose we'll address that in http://projects.theforeman.org/issues/6590.