updated: camera controller classes
changed: the demo, esp. graphics demo

Added a new class, DemoSwitcher, which is derived from GraphicsApplicationBase.
The DemoSwitcher instance has a pointer of the demo's base class, and is used to control demos.
Disabled the incremental link to avoid the following error:
LINK : fatal error LNK1123: failure during conversion to COFF: file invalid or corrupt
changed: the demo, esp. graphics & physics demo

Added a new class, DemoSwitcher, which is derived from GraphicsApplicationBase.
The DemoSwitcher instance has a pointer of the demo's base class, and is used to control demos.
updated: the physics demo source code.