Started work on the Pandora's keyboard input

|SOURCE|
[Common/InputDevice]
* Changed the GAMEPAD_BUTTON_* constant names to better reflect the Pandora's
  button input
* Added AURA_KEY_* constants to expand the keyboard input to the A-Z
  characters, 0-9, and F1-F12 keys
[Common/Keyboard]
* Added a file descriptor for the keypad on the Pandora
* Removed the Initialise, Terminate, and GetState member funcitons from the
  common source to be platform-specific
[Common/Game]
* Added checks for the window and input manager's memory allocation
* Changed the gamepad quit button to select
[Common/Gamepad]
* Added a table to map code values to button values from the gamepad hardware
* Changed the press/release to use the table for code values to button values
  to set the button states
[Pandora/PandoraInputManager]
* Much like the Linux version, the PandoraInputManager maintains device state,
  though as the functionality is programmed in the device for the Pandora, this
  is largely useless
[Pandora/Game]
* PreInitialise initialises the InputManager instance to be a
  PandoraInputManager instance
[Pandora/Keyboard]
* Added a table to map code values to the key values they represent
* Initialise finds the keypad device for input, if it can't find it an error
  code is returned
* GetState acts much like the Gamepad and uses select to grab whatever state is
  available, returning immediately, then the code values are mapped to keys
  which are kept internally with m_KeyState.Keys
Added the missing Linux keyboard member functions

|SOURCE|
[Common/Game]
* Moved the gamepad and keyboard initialisation to the Initialise member
  function
* Using the keyboard state instead of the IsKeyDown member function for the
  keyboard
[Common/Keyboard]
* The connected member variable is set to false in the constructor
[Linux/Keyboard]
* Added the member function definitions which were absent in the wake of
  re-organising the code