ENH: Removes HTML folder and resource duplication, if html path empty.

[dvbridges]

No description provided.

[coveralls]

Coverage increased (+0.3%) to 48.129% when pulling 2179c77 on dvbridges:flattenHTML into 81fb15f on psychopy:master.

[codecov-io]

Codecov Report

Merging #2687 into master will increase coverage by <.01%.
The diff coverage is 47.36%.

@@            Coverage Diff             @@
##           master    #2687      +/-   ##
==========================================
+ Coverage   43.77%   43.78%   +<.01%     
==========================================
  Files         236      236              
  Lines       44325    44321       -4     
  Branches     7530     7530              
==========================================
- Hits        19405    19404       -1     
  Misses      22916    22916              
+ Partials     2004     2001       -3

Impacted Files	Coverage Δ
psychopy/experiment/_experiment.py	51.43% <100%> (+0.28%)	⬆️
psychopy/experiment/flow.py	76.16% <100%> (-0.25%)	⬇️
...sychopy/experiment/components/settings/__init__.py	72.03% <100%> (+0.08%)	⬆️
psychopy/app/builder/builder.py	52.63% <9.09%> (+0.13%)	⬆️
psychopy/visual/textbox/fontmanager.py	71.18% <0%> (-0.7%)	⬇️
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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