Joysticks support and some networking improvements

Recent changes:

• New Phong-rim material is now a default one for meshes.
• Full support of Xbox 360 gamepad.
• Support of standart PC joysticks and wheels (no force feedback is available yet).
• Fixed clip planes for all APIs (no more problems with 2D reflections).
• Optimization of shadow map memory usage.
• GUI refactoring, all widget classes now have "Widget" prefix, like WidgetVBox (use deprecate.h for backward compatibility).
• Visual limits of suspension travel in JointWheel.
• New WidgetMenuBox and WidgetMenuBar widgets.
• Mask buffers for GUI rendering (WidgetSprite).
• Fixed reading of empty string arrays from XML.
• Dedicated thread for networking in the engine.
• New Packet class for parallel data transfer in the thread.
• Added a lot of articles in "Content Creation / Materials" section of the documentation.

Here is a screenshot from the small racing demo, which will be included into Unigine SDK soon (there are both types of gear box available, physics interaction of objects, and some GUI elements, including minimap and speedometer):