Add support for touch and gesture events for supported mobile webkit platforms.
Extract common implementation and interface out of MouseEvent into HumanInputEvent.

Review at http://gwt-code-reviews.appspot.com/867801

Review by: jgw@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9287 8db76d5a-ed1c-0410-87a9-c151d255dfc7