[#201] [Core] AudioBus - support for multiple node connections and mixed amount of channels

[michalsek]

Closes #201
Closes #172

Introduced changes

• Multi-node support through up-down mixable AudioBus implementation and internal node buses.
• Fix issues with memory allocation and de-allocation by:
  • restricting internal graph connection changes to be done only when holding a graph mutext, as well as only at the begining of the render quantum.
  • Creating AudioNodeManager which keeps references to source nodes as well as nodes that has pending connection change (wait for connect or for disconnect)
• Fixes some minor issues or typos
• Improves AudioBufferSourceNode performance by taking advantage of memory operation as much as possible

Checklist

• Linked relevant issue
• Updated relevant documentation
• Added/Conducted relevant tests
• Performed self-review of the code

[maciejmakowski2003]

Amazing work!!!🔥