user upgrades: update upgrade landing page.

* Add a frequently asked questions section.
* Add nicer looking upgrade buttons.
* Format the page nicer.
* Prevent users from attempting invalid upgrades on users that are
  already Platinum or above.

app/controllers/user_upgrades_controller.rb

@@ -1,15 +1,18 @@
 class UserUpgradesController < ApplicationController
-  helper_method :user
   respond_to :js, :html
 
   def create
-    @user_upgrade = authorize UserUpgrade.create(recipient: user, purchaser: CurrentUser.user, status: "pending", upgrade_type: params[:upgrade_type])
+    @user_upgrade = authorize UserUpgrade.create(recipient: recipient, purchaser: CurrentUser.user, status: "pending", upgrade_type: params[:upgrade_type])
     @checkout = @user_upgrade.create_checkout!
 
     respond_with(@user_upgrade)
   end
 
   def new
+    @user_upgrade = authorize UserUpgrade.new(recipient: recipient, purchaser: CurrentUser.user)
+    @recipient = @user_upgrade.recipient
+
+    respond_with(@user_upgrade)
   end
 
   def show
@@ -17,7 +20,9 @@ class UserUpgradesController < ApplicationController
     respond_with(@user_upgrade)
   end
 
-  def user
+  private
+
+  def recipient
     if params[:user_id]
       User.find(params[:user_id])
     else