Support Users Directly Uploading Profile Pictures.

* Adds a `picture` attribute to `User`.
* Preserves Gravatar as a fallback option.
* Now, you should use `user.profile_picturer` instead of `gravatar_url`
* TODO: Ensure `profile_picture` handles sizing right for uploaded images.

app/controllers/users_controller.rb

@@ -24,8 +24,8 @@ class UsersController < ApplicationController
 
   private
 
-    # Only allow a trusted parameter "white list" through.
-    def user_params
-      params.require(:user).permit(:name, :biography, :nickname, :affiliation)
-    end
+  def user_params
+    params.require(:user).permit(:name, :biography, :nickname, :affiliation,
+                                  :picture, :picture_cache)
+  end
 end