Continue to optimize performance

[SamGRosen]

Currently the performance is good, but it could be better, as current features were implemented with an MVP mindset. Some possible optimizations:

• Use of TRIANGLE_FAN when rendering circle points
• Use of TRIANGLE_STRIP when rendering area plots TRIANGLE_STRIP and FAN will actually lower performance due to an inability to do batch draw calls as each mark drawn with a strip or a fan will require an individual draw call.
• Switch to WEBGL2 (create vertex array, upgrade shaders) Completed in Add arc mark type #21
• Use index buffers to avoid creating duplicate vertices