feat(ngMobile): add ngMobile module with mobile-specific ngClick

Add a new module ngMobile, with mobile/touch-specific directives.
Add ngClick, which overrides the default ngClick. This ngClick uses touch
events, which are much faster on mobile. On desktop browsers, ngClick
responds to click events, so it can be used for portable sites.
chore(docs): add angular-mobile.js to index.html