Opera 14 / WebKit detection

Added detection for Opera Mobile on Android which uses the newly announced WebKit engine. This makes it detected as Chrome Mobile instead of Opera Mobile.

See http://my.opera.com/ODIN/blog/2013/03/05/opera-14-beta-for-android-is-out

I'm assuming that Opera for desktop will also include OPR/<major>.<minor>.<patch> in the user agent string but it might be to soon to add support for that.