Timeline - Refactor using PixiJS and frame-times

[Joery-M]

Currently the timeline is implemented using native canvas. My original idea was that this was fine, but after thinking about it, interactions would be very difficult.

Currently all positions are tracked using milliseconds, but after working on #24, I realised that the items suffer from precision issues when moving. This would only get worse when using framerates like 23.976 fps.

Requirements:

• Change the rendering from native canvas to using PixiJS.
• Change how time is tracked from milliseconds to frames.