account based feeds

The system now supports per-user account based feeds. This comes with
all the bells and whistles of generic account management:

- Signup/Login
This is done via email links. Right now the links don't do anything,
they simply display on screen and you navigate to them. Eventually we'll
set up postfix/sendgrid or something like that.

- All endpoints are now protected requiring a user to be logged in via
the magic email link/one-time code.

- A new home page that explains a bit about the project and gives you
the ability to signup/login.

- All feeds/feed-items are scoped to a user. We are definitely not doing
this optimally. Each feed is stored per-user.. if two users add the same
feeds.. then they get stored twice. We can address this if it actually
starts to become a problem.