Force usage of HTML5 for embedded videos

This works by adding html5=1 to the uri and is done using http request events.
For this purpose the new URIChanger wrapper has been implemented similar to the
already existing UserAgentChanger.

Signed-off-by: Klemens Schölhorn <klemens@schoelhorn.eu> (some improvements)
Merge remote-tracking branch 'klemens/master'

Conflicts:
	lib/URIChanger.js
	lib/main.js