Complete Facebook registration/login feature TODOs

[bigpopakap]

Complete the detailed parts of the feature. This means addressing the TODOs in the code in FbAuthAction.java

[bigpopakap]

https://developers.facebook.com/docs/howtos/login/getting-started/

[bigpopakap]

Should use the server-side login instead: https://developers.facebook.com/docs/howtos/login/server-side-login/#step1

[bigpopakap]

Here's a module that can make things easy woo! http://www.playframework.com/modules/fbconnect-0.1/home (edit: this module is actually only for Play versions 1.x, so poop)

[bigpopakap]

Borrowing comment from #49:

Next things to do:

• (done) figure out how to store sessions and stuff in the context, so the fbapi object can also be stored there
• (done) comment the fbapi class
• (done) change all references to the current SessionModel with AppCtx.Session.get()
• (done) create the user object
• (done) clean up the code
• (done) address TODOs
• (done) refactor code if necessary (#32, #33, #34, rename Doers to something better)

Also, these TODOs from #53

• (done) Add a TODO to test that no class invokes Ebean.save() etc. directly
• (not going to do) Add some way to manage transactions in BaseModel (or at least a TODO to do so)