migrated javascripts to coffescript
Moved to haml in preferece to erb for views
declare show_loading and hide_loading as window global functions,
to make them available for gadgets/index.js.coffee.
Unless done, brakes before_ajax function and leads to plain :get request
where xhr :get expected, which results in ActionController::InvalidCrossOriginRequest exception
coffescript cleanup with helper functions on layout level to keep js DRY