Add guides for "Creating a SPA" and "Setting up an API server"

[crandmck]

These are similar to the MBaaS guide of #747, and should cover the basic steps to create each type of app, with links out to the articles that have more details. Really, we need example apps that the doc could follow, but failing that, it could just provide an overview and general procedure. Presumably, these would use the AngularJS client.

NOTE: Moved from https://github.com/strongloop-internal/scrum-loopback/issues/40