Create "force-pushable" equivalent for Ammo.js examples

[diarmidmackenzie]

Several Cannon examples use the force-pushable event, which allows you to click on items and give them a push.

Same thing would be useful for Ammo examples

1. to allow more testing
2. to show how to use the Ammo APIs to do this kind of thing.

This issue tracks building such a component, and building out a set of Ammo examples that make use of it and/or adding it to existign Ammo examples.

[diarmidmackenzie]

Fixed in #11