[MultiInstance] Use same input stream in multiple instances

[Bluscream]

Example usecase:

• Customer 1 starts playing http://domain.com/stream.mp3
• Customer 2 starts playing http://domain.com/stream.m3u which invokes /stream.mp3
• Bot realizes that the requested stream is already playing and uses that input stream.

This would with even only 2 users of the stream reduce download bandwith usage by 50%

[Bluscream]

Maybe this could also work with Youtube audio but im unsure how much of the yt vid is cached.