BF: Double buffer panels/fix high DPI error on Windows <8.1

[mdcutone]

When creating a new loop or collapsing component panes, either the control flickers when moving the mouse around or only partially redraws. This PR double buffers the controls providing a smoother visual experience (on Windows at least).

Also includes a bugfix for #2818.

[coveralls]

Coverage increased (+0.03%) to 48.68% when pulling 48710a5 on mdcutone:builder-fixes into 3e8adf5 on psychopy:master.

[codecov-io]

Codecov Report

Merging #2820 into master will increase coverage by <.01%.
The diff coverage is 22.22%.

@@            Coverage Diff             @@
##           master    #2820      +/-   ##
==========================================
+ Coverage   44.45%   44.45%   +<.01%     
==========================================
  Files         242      242              
  Lines       45030    45034       +4     
  Branches     7650     7650              
==========================================
+ Hits        20018    20020       +2     
+ Misses      22955    22953       -2     
- Partials     2057     2061       +4

Impacted Files	Coverage Δ
psychopy/app/_psychopyApp.py	36.59% <0%> (-0.14%)	⬇️
psychopy/app/builder/builder.py	52.18% <100%> (+0.03%)	⬆️
psychopy/app/builder/flow.py	35.99% <100%> (+0.1%)	⬆️
psychopy/visual/textbox/__init__.py	43.6% <0%> (ø)	⬆️
psychopy/app/builder/dialogs/dlgsConditions.py	7.51% <0%> (ø)	⬆️
...ychopy/localization/generateTranslationTemplate.py	0% <0%> (ø)	⬆️

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