audiobargraph: avoid heap allocation
audiobargraph: check allocation
audiobargraph: stick to single precision
audiobargraph: fix callback crash due to missing initializer
audiobargraph: use variable & callback for alarm state (refs #9491)
audiobargraph: use variable & callback for audio values (refs #9491)

Also fix potential buffer overflow with snprintf().
audiobargraph: remove bogus TCP connection (fixes #9491)