- Fixed some potential deadlocks and issues in the client thread concurrency control
- Fixed client connection potentially being released before the client thread exit
- Added a warning print if the server doesn't get a steady clock
- Changed pending sample buffer to std::deque for improved
  efficiency on high sampling rates. Updated the plugin interfaces accordingly.
- Removed the truncation of the drift measure to zero, no longer
  needed as the GUI view is less often updated
- Added several sampling rates (including high freqs such as 44100)
  to Generic Oscillator for debugging.
- The server will now clear the pending buffers on pressing 'Stop'.
- Changed some iterator definitions to 'auto' for clarity
- Fixed gcc warnings about %llu and uint64
- Added some comments
- Code cleanup