Implement common way to notify users on errors and information messages

1. create method (static) to put text message(s) in session with given name
2. display this message(s) on each page (if message(s) exists)
3. remove message(s) from session when request (to page where message displayed) completed (using filter?)
at the end we should have method like: flash("trololo"); and it will be displayed on the page. and when user refreshes this page it should disappear