FEATURE: Add basic support for Safe Mode

In Safe Mode all JS extensions and site customizations are disabled.

To access Safe Mode visit `sitename.org/safe-mode`

app/controllers/safe_mode_controller.rb

@@ -0,0 +1,20 @@
+class SafeModeController < ApplicationController
+  layout 'no_ember'
+  skip_before_filter :preload_json, :check_xhr
+
+  def index
+  end
+
+  def enter
+    safe_mode = []
+    safe_mode << "no_custom" if params["no_customizations"] == "true"
+    safe_mode << "no_plugins" if params["no_plugins"] == "true"
+    safe_mode << "only_official" if params["only_official"] == "true"
+
+    if safe_mode.length > 0
+      redirect_to path("/?safe_mode=#{safe_mode.join("%2C")}")
+    else
+      redirect_to :index
+    end
+  end
+end