STREAM_GAMECONTROLLER_IGNORE_DEVICES and STREAM_GAMECONTROLLER_IGNORE_DEVICES_EXCEPT environment variables provide the same functionality as SDL_GAMECONTROLLER_IGNORE_DEVICES and SDL_GAMECONTROLLER_IGNORE_DEVICES_EXCEPT, with the difference being SDL_* variables take effect at all times (UI and streaming) while STREAM_* variables take place only while streaming.
Fixes#425