[Content] MVP: draw and create an object

[snowymo]

Is your feature request related to a problem? Please describe.
Shall we have a minimal sample that the user can use controller/mouse click to create an object?

Describe the solution you'd like

1. Probably our final presentation will include content creation.
2. Let's have a minimal sample for infrastructure to test. For example, the user can draw some paths, and metaroom reacts with displaying maybe shapes, maybe 3D objects.
3. For easy debug, it'd be better to support mouse input and controller support together.

[4]. We want to test if other clients can see the same drawing, without syncing all the drawing information but the input events.

[snowymo]

@kenperlin @keruwang
Since clay is way more complicated than drawing lines, we probably need to
either 1) integrate the latest version into this repo.
or 2) extract similar but simpler functionality that for me to experiment.

We have to have multiple clients see the same thing because the video we want to make includes two clients: a teacher in VR and a student on the screen. I guess a backup plan is that we record everything in advance.