Create kinematics shoot and drop world

Okay, I had to make a few changes to better support what you are doing here; and to better merge with the most recent main branch that uses Aframe 1.2.0.

So a heads up:

We are using a modified aframe-physics now. One that works with Aframe 1.2.0.
I noticed that you were attaching properties to the a-scene entity; but my injected code was overwriting it. I changed it so that you can now add properties after i.e., background colour; but now note you should add your own lights so that you get the effect you like as the renderer we use set physicallyCorrectLights to true. I changed this in all your physics worlds.

I changed the name of some of the circles API calls i.e.,

<!--  NOT <a-scene circles_properties>, BUT RATHER -->
<a-scene circles_scene_properties>

and

<!--  NOT <circles-avatar/>, BUT RATHER -->
<circles-manager-avatar/>

This also includes adding a new component for the "user gesture/enter UI" just after body (see the updated readme.md for the changes and placements).

<!-- right after the enter <body> tag --> 
<circles-start-ui/>

Everything looks good now but some stuff we may have to check out.

There is floating confetti in front of the cannon (shoot and drop)
The cupboard no longer stops the ball (shoot and drop). Is this intended? I notice there is now a physics error that may be related to this ...
The bear height still needs to be fixed in this PR (freefall)

PlumCantaloupe / circlesxr

Create kinematics shoot and drop world #98

Shoot and Drop experiment