Debug: add user timings to retro channel join
Debug: add user timings to retro channel join

  - I'm seeing bizarrely long waiting times——> 300ms——in development (i.e. no latency) between retroChannel.join() and the channel client's receipt of 'ok'. adding some console.{time,timeEnd} calls to get a signal as to whether this is also happening in minified/optimized builds
    - there is a small set of database queries in RetroChannel.join/4, however even when I remove these queries, hardcoding the retro state, the join time is still greater than 300ms 🤔

stride-nyc/remote_retro,stride-nyc/remote_retro,stride-nyc/remote_retro