System framework improvements

The System's code has had a lot of iterations to it which i do wish i could have gotten to quicker, but it's definitely worth it. It is now a lot slimmer, removing two classes (four source files) without losing any features.

When i first wrote the code it became large because i wanted to make it very flexible. I have now removed redundant code and cleaned it up a lot. The System's code needs to be fast and very solid as its the base for a lot of the engine and its plug-ins. These latest changes should be the last major ones made on these classes now (at last!!).

As it stands we now have:

• TaskThread - Wraps a thread and provides processing of tasks
• SystemGroup - Manages a group of System's and enforces a specific start up and tear down sequence for each System registered to it, as well as periodical updates (ticks).
• System - Allows a class to be managed by a SystemGroup and receives ticks.

Each SystemGroup uses a single TaskThread to process its tasks. This provides the main part of the multi-threaded framework.

We had a problem where we would get 50fps in the samples even though they were set to be ticked at 60fps (as well as any movements in the fps sample would causes large frame rate decreases). This problem has disappeared now due to these changes, getting a very stable frame rate even whilst moving around. It is also responsive to small changes in tick intervals.

Ticking the graphics system at 16.6666667 gives a frame rate of 60fps and a tick interval of 16 gives a frame rate of 62fps. Obviously this is what it should do, but it does suggest (i still need to profile to get proof) that there is a very low latency between the primary thread waking up and all of the Systems being ticked.

My next aims are to provide built-in debugging code/features to help with development (especially to track down threading and release mode issues) and possibly improve memory management, as there are a few places where we are allocating and freeing memory a lot.