Data: Add view with nextId as key

We want to search for duplicate nextIds, and
this will help us do that.
Multiple clients can create stories

Handle requests to create stories from
multiple clients by moving the first-story
calculation to the server side.

Works for situations where people are just
adding stories to the top of the backlog.

Does not work for situations where a story
is added on client A, moved, and a new
story is added on client B.
Data: Ignore requests to delete old stories

Do not care if people request to delete stories
that have already been deleted. Just tell
them things are fine, because they are.
Add naive story-move function on server

Start the process of putting the story-move
functionality on the server. This commit is
a bit sloppy, but it moves the ball forward
a little bit.

Side effect: Stories now have "last" as their
nextId if they are the last story in the
backlog, rather than being undefined.
Complete the naive story-move function on server

We can now move stories around on the server side,
albeit in a naive way that assumes database operations
will always succeed.