(as the critcal label is not setup yet please consider this PR as critical)

Related to:

• System Update Scheduler #66

I have modified the way we handle system running by adding schedulers.

The schedulers work by implementing a common interface that simply needs the call operator operator()(Registry &reg). Each scheduler is responsible for running the systems the way intended.
We can get a scheduler by using the GetScheduler method from the registry. This is useful if the scheduler is based on time, for example, the FixedTimeScheduler.

I have implemented two basic schedulers Startup and Update : startup will only execute the systems once and update is the classical way of running systems (each time we call the RunSystems function).

I have also implemented two time based schedulers FixedTimeUpdate and RelativeTimeUpdate.

Fixed time works by only calling the systems when needed and doing multiple runs if the framerate doesn't meet the tick rate of the scheduler. By default the tickRate is 20ms (frame time when running at 50FPS). With this scheduler, the systems will only run 50 times per second even if the framerate is higher. There is a method to get the FixedDeltaTime.

Relative time works by calling the systems based on a target tickRate. If the client manages to run at the given tickRate or higher, the systems will always run once, but if the target tickRate isn't met the systems will run multiple times, taking into account the whole deltaTime the frame took. With this scheduler, systems always run at least once and will run multiple times if needed. There is a method to get the current deltaTime we should use for computations.

I have also modified the soft body simulations to use the RelativeTimeScheduler, as I find it the most appropriate.