Improve audio streaming

[marcelveldt]

• Refactor stream controller
• Only use multi subscriber logic when really needed (sync groups)
• More robust handling of misbehaving clients (dlna, kodi etc) that do multiple GET requests per session
• Speed improvements
• Foundation for Core controllers abstraction with configuration options
• Split off stream webserver from regular webserver
• Fixed some possible eventloop blockages
• Fixed some race conditions
• An awful lot of other improvements