Enhance vector drawing library in sorna-media

[achimnol]

We have a very early implementation of vector drawing library in sorna-media. It allows users to write drawing codes in Python but see the result in the browser in codeonweb.com. Currently we use a home-brew Javascript library that parses msgpack'ed data generated by sorna-media Python library and render shapes using fabric.js.

It currently supports drawing of simple lines, rectangles, circles, and triangles with some color and line widths, and animation by translation, fade in/out, etc.

• Goal 1: Refactor the current Javascript/Python libraries composed of monolithic long bodies of functions so that we can add new features with ease.
• Goal 2: Extend the drawing API for more various types of shapes such as bezier curves and text outputs. Also add support to specifying more detailed shape attributes such as patterns and gradients as well as animation of such various attributes.
• Goal 3: Implement/port turtle API over the drawing API.

As long as you keep the compatibility of the user-facing Python API (which of course requires a lot of extension), all implementation details are fully up to you!

[achimnol]

This drawing API is still there, but we no longer use it in our primary product Backend.AI. We will revisit this later when we need it.