Made the first half of running the application through game modes/states.

- I moved the different Mode class to be handled through the ModeManager class
- I started merging EditorContext with EditorMode as the context does only few more
  and should handled within the same class.
- The same will be done with GameMode.
- I renamed IsInGame() to IsConnected() as it is what it does actually check.
  Plus, it was mistakenly used a editor mode checker sometimes.
- I moved several inits uselessly done outside a class within the class itself
  while seeing it.
- I removed the *State stub classes as their equivalent counter part is done
  in the *Mode classes.
- I renamed the ModeContext class to InputManager since it's what it does,
  and moved the variable used to change the game mode to within the ModeManager.
  I also made the OIS deinit be done in the input manager where it belong.
- I dropped the camera moving behaviour when going near the screen edges
  as it came in the way when playing.

This needs more tests before going further.