Add frame rate limitation

[GCeSilva]

Problem

Right now we have no manner of limiting the frame rate at which cubos is run.
It would be optimal if we could limit it to, for example, 60fps, instead of relying on vsync, which will not always prove effective, as more powerful systems might bring out more fps then desired.

Ex: system outputting 400 fps while physics are only updated every 15 frames.