Get stories from the server

Add a rough stories API to the server, and
use it on the client.
Make stories list an object instead of an array

As we prepare to re-order the list of stories all
over the place, it maybe makes more sense to have
the list of stories be an object rather than an
array.
Backlog: Add notion of sort index

Add a sort-index property to stories, and incoporate
it to the act of adding new stories to the backlog.
Backlog: Adjust sort index as list is re-ordered

Update the sort index of the dropped element to be
halfway in between the elements it is dropped between.