PERF: stop loading handlebars and ember compilers in prod

(this removes a nice 50K from our initial payload and saves memory)

Also fixes invalid HTML automatically if added to HEAD or /BODY

db/migrate/20151126233623_add_baked_head_and_body_to_site_customizations.rb

@@ -0,0 +1,6 @@
+class AddBakedHeadAndBodyToSiteCustomizations < ActiveRecord::Migration
+  def change
+    add_column :site_customizations, :head_tag_baked, :text
+    add_column :site_customizations, :body_tag_baked, :text
+  end
+end