Swiping slider doesn't work about material.angular.io

[mmalerba]

This is caused by angular not recognizing that HammerJS is loaded (following warning can be observed in the console: Could not find HammerJS. Certain Angular Material components may not work correctly.)

@jelbourn This can be fixed by removing async on the HammerJS script, though maybe we should try to detect when HammerJS loads late and enable swipe support?

[jelbourn]

@mmalerba The latter would be nice. @crisbeto any thoughts?

[crisbeto]

It makes sense to check for Hammer when we try to bind something, instead of the constructor. I'll play around with it and put in a PR.