Fix 2 bugs and refactor RunningMeanStd to support dict obs norm

[Trinkle23897]

close #672, #688, #689, #691

[codecov-commenter]

Codecov Report

Merging #695 (b96cfb0) into master (6505484) will increase coverage by 0.16%.
The diff coverage is 93.75%.

@@            Coverage Diff             @@
##           master     #695      +/-   ##
==========================================
+ Coverage   93.25%   93.42%   +0.16%     
==========================================
  Files          72       72              
  Lines        4890     4894       +4     
==========================================
+ Hits         4560     4572      +12     
+ Misses        330      322       -8     

Flag	Coverage Δ
unittests	93.42% <93.75%> (+0.16%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
tianshou/env/worker/ray.py	76.59% <0.00%> (ø)
tianshou/data/collector.py	94.24% <100.00%> (ø)
tianshou/env/venv_wrappers.py	83.33% <100.00%> (-2.39%)	⬇️
tianshou/env/worker/dummy.py	76.47% <100.00%> (ø)
tianshou/env/worker/subproc.py	87.02% <100.00%> (ø)
tianshou/utils/statistics.py	100.00% <100.00%> (ø)
tianshou/utils/logger/tensorboard.py	95.45% <0.00%> (+20.45%)	⬆️

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