Fix issue with time tracking.
Fix issue with time tracking.

When GetTickCount returns large values (e.g. on Windows 10, even after just booting up) it causes floating point resolution problems with time tracking, causing the simulation to run sluggish.

Issue was fixed by taking the reference tick count at program start and returning values relative to that, ensuring the values will always be "small".

GlyphXTools/particle-editor,GlyphXTools/particle-editor