* Add a camera view event handler. The event script is called when the camera view changes.
* The argument of the called function is stored in the _this variable and has as first element the new camera mode. Possible arguments are ["INTERNAL"], ["EXTERNAL"], ["GUNNER"] and ["GROUP"].
*
* Argument:
* 0: Code to execute (Code or String)
*
* Return value:
* ID of the event script (used to remove it later).