Refactor user controller, create action, mostly.

The gist of the commit are a few improvements in the
create action, where:

* long boolean statemenst have been wrapped in smaller more readable
  methods.
* the 3rd party user info creation has been extracted (still in controller)
* a small helper method for creating a new user from params (to reduce
  visual clutter)
* specs have been added where I came across untested methods/branches

Other changes are more trivial like formatting and whitespace fixes.
Hope this helps. Regards.

app/models/user.rb

@@ -102,6 +102,15 @@ class User < ActiveRecord::Base
     find_available_username_based_on(name)
   end
 
+  def self.new_from_params(params)
+    user = User.new
+    user.name = params[:name]
+    user.email = params[:email]
+    user.password = params[:password]
+    user.username = params[:username]
+    user
+  end
+
   def self.create_for_email(email, opts={})
     username = suggest_username(email)