Implement TouchEvent internals; add Touch
Implement TouchEvent internals; add Touch

This change adds support for all TouchEvent fields, including those
of TouchList type. It also comes with support for Touch (element of
TouchList).

References:

-	https://developer.mozilla.org/en-US/docs/Web/API/TouchEvent
-	https://developer.mozilla.org/en-US/docs/Web/API/TouchList
-	https://developer.mozilla.org/en-US/docs/Web/API/Touch

GitHub-Pull-Request: dominikh/go-js-dom#55
dominikh/go-js-dom