[Enhancement] Add Filters to Two.js

[jonobr1]

Is your feature request related to a problem? Please describe.
Both SVG and Canvas APIs have the ability to filter the rendering style of the content displayed. Take those along with custom shaders for the WebGL renderer to incorporate filtering into Two.js.

Describe the solution you'd like

var group = two.makeGroup();
group.add(circle, star, rectangle, path);
group.filter = 'blur(10px)';
star.filter = 'contrast(175%)'

Additional context
Filter specifications on MDN: https://developer.mozilla.org/en-US/docs/Web/CSS/filter