Discovery for the media tools: the active image model and remaining image allowance, the video models this account ma...

Discovery for the media tools: the active image model and remaining image allowance, the video models this account may use with their per-second prices and prepaid wallet balance, and every valid slideshow style, template, and collection id. Call this before generate_image / generate_video / generate_slideshow instead of guessing enum values. Spends nothing.