Replace nwb to enable testing through jest

[frontendphil]

• removes nwb
• adds preconstruct
• adds webpack and webpack-dev-server with the respective config
• removes gh-pages
• adds now to deploy example page

[codecov-io]

Codecov Report

Merging #337 into master will increase coverage by 2.8%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master     #337     +/-   ##
=========================================
+ Coverage   71.05%   73.86%   +2.8%     
=========================================
  Files          22       22             
  Lines         501      574     +73     
  Branches        0       90     +90     
=========================================
+ Hits          356      424     +68     
- Misses        145      149      +4     
- Partials        0        1      +1

Impacted Files	Coverage Δ
src/Mention.js	55.55% <0%> (-6.95%)	⬇️
src/utils/combineRegExps.js	100% <0%> (ø)	⬆️
src/utils/readConfigFromChildren.js	88.88% <0%> (ø)	⬆️
src/LoadingIndicator.js	0% <0%> (ø)	⬆️
src/utils/getMentions.js	100% <0%> (ø)	⬆️
src/utils/getPlainText.js	100% <0%> (ø)	⬆️
src/Highlighter.js	98.3% <0%> (+0.38%)	⬆️
src/Suggestion.js	85.18% <0%> (+3.36%)	⬆️
src/MentionsInput.js	60.28% <0%> (+5.96%)	⬆️
src/SuggestionsOverlay.js	59.18% <0%> (+7.83%)	⬆️

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[vercel]

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