Make oauth optional
Allow the python client to be run without app engine

This is quite a hacky mess right now. Further changes will clean up the
app engine dependencies and abstract out some of the complications.
Use the get readset method to pull in sequence data
Remove user settings for the backend

Instead, provide a backend parameter on all requests, and allow the
user to select which backend to search over in the readset choosing
dialog.
Remove urlfetch as its unused
Add very basic client-side only pagination for readsets