Data: Use processing queue for new stories

Put add-story requests into a queue for
processing serially in the order they
were received.

This solves the 3-requests-at-once problem.
Data: Callback when story is added

Use the event emitter to tell the caller
when a story has been processed in the
add-queue.

Also 'addStoryProto' is now the new 'addStory'
Backlog: Add test for add story

Also clean up the callbacks a little bit
for adding new stories.