Native threaded concurrency

[jtc42]

Switches to native threading for concurrency, and uses labthings/flask-threaded-sockets for websocket support.

[codecov]

Codecov Report

Merging #120 into master will decrease coverage by 1.03%.
The diff coverage is 80.95%.

@@            Coverage Diff             @@
##           master     #120      +/-   ##
==========================================
- Coverage   92.75%   91.72%   -1.04%     
==========================================
  Files          46       46              
  Lines        1863     1836      -27     
  Branches      306      312       +6     
==========================================
- Hits         1728     1684      -44     
- Misses         88       99      +11     
- Partials       47       53       +6     

Flag	Coverage Δ
#unittests	91.72% <80.95%> (-1.04%)	⬇️

Impacted Files	Coverage Δ
src/labthings/sockets.py	71.42% <ø> (-22.96%)	⬇️
src/labthings/view/__init__.py	83.80% <0.00%> (-0.12%)	⬇️
src/labthings/tasks/thread.py	84.86% <71.79%> (-14.07%)	⬇️
src/labthings/tasks/pool.py	87.50% <83.33%> (+5.50%)	⬆️
src/labthings/default_views/actions.py	100.00% <100.00%> (ø)
src/labthings/default_views/tasks.py	100.00% <100.00%> (ø)
src/labthings/labthing.py	97.01% <100.00%> (ø)
src/labthings/sync/event.py	94.11% <100.00%> (-1.13%)	⬇️
src/labthings/sync/lock.py	90.80% <100.00%> (-1.04%)	⬇️
src/labthings/utilities.py	100.00% <100.00%> (ø)

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