Knobs: add escapeHTML option; use it by default in Vue, Angular, and Polymer

[Hypnosphi]

Issue: #3471

Those frameworks allow rendering of plain HTML, so user input should be escaped

[codecov]

Codecov Report

Merging #3473 into master will increase coverage by <.01%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master    #3473      +/-   ##
==========================================
+ Coverage   37.56%   37.56%   +<.01%     
==========================================
  Files         459      459              
  Lines       10235    10237       +2     
  Branches      914      920       +6     
==========================================
+ Hits         3845     3846       +1     
- Misses       5829     5850      +21     
+ Partials      561      541      -20

Impacted Files	Coverage Δ
addons/knobs/src/angular/index.js	0% <ø> (ø)	⬆️
addons/knobs/src/polymer/index.js	0% <ø> (ø)	⬆️
addons/knobs/src/vue/index.js	24.13% <ø> (ø)	⬆️
addons/knobs/src/react/WrapStory.js	57.44% <0%> (ø)	⬆️
addons/knobs/src/base.js	10.52% <0%> (-0.59%)	⬇️
addons/knobs/src/KnobManager.js	85% <100%> (+0.78%)	⬆️
.../viewport/src/manager/components/RotateViewport.js	22.72% <0%> (ø)	⬆️
addons/info/src/components/types/proptypes.js	88.88% <0%> (ø)	⬆️
addons/actions/src/lib/types/infinity/index.js	80% <0%> (ø)	⬆️
...modules/ui/components/stories_panel/text_filter.js	36.11% <0%> (ø)	⬆️
... and 69 more

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