Corrected usage of subscription helper.
Corrected usage of subscription helper.

The subscription helper makes use of singular nouns: 'story',
'project_group', etc, while the events are being broadcast using
the plural 'stories', 'project_groups', etc, extracted from the
request url. As a result, subscriptions were not being handled
properly, as project_groups would drop out entirely, and
timeline_events were not supported by the subscription helper.

Change-Id: I96152ead1e616fcfd96fd4168a13abf07695b5da

ColdrickSotK/storyboard,ColdrickSotK/storyboard,ColdrickSotK/storyboard