WICKET-5517 IE11 returns false for Wicket.Browser.isIE()

Add a simple check whether the current user agent is IE 11.
It is not used by Wicket for now

(cherry picked from commit dfd12188a0da8cdc37aecbd29fc83fddfcb51c4d)
Print the processes markup when an error with opening/closing tag is detected for easier debugging.
Add Apache Licence header