Design and implement input subsystem

[Witek902]

The system should detect and access all avialable input devices like:

• mouse
• keyboard
• gamepad/joystick
• VR devices (Oculus Rift HMD system, Vive/Touch controller system, etc.)

The API will be exposed for the user, so it must be well documented. Adding a new device (or device type) should't require serious changes. So the input messages should be very generic, for example:

• mouse movement - 2d int
• gamepad analog stick - 2d float
• Vive/Touch position - 3d float
• etc...

Materials:

• http://www.gamedev.net/page/resources/_/technical/general-programming/asynchronous-keyboard-input-for-fixed-time-step-games-r3959
• https://msdn.microsoft.com/en-us/library/ee418864(v=VS.85).aspx

TODO List (only on Windows; Linux version should come when nfCore is buildable on Linux):

• [ ] Base of Input system in nfCore/Input
• [ ] InputManager base class and backends:
  • [ ] Keyboard/mouse
  • [ ] Controller (XInput)
• [ ] Event mapping (key to event)
• [ ] Collection of default events (move, rotate camera etc)