Translate package from CoffeeScript to ES6

[joefitzgerald]

This PR translates all CoffeeScript to ES6, and makes use of the fbjs eslint preset.

• [x] file-view.coffee > file-view.js
• [x] get-tags-file.coffee > get-tags-file.js
• [x] go-back-view.coffee > go-back-view.js
• [x] go-to-view.coffee > go-to-view.js
• [x] load-tags-handler.js > load-tags-handjs
• [x] main.coffee > main.js
• [x] project-view.coffee > project-view.js
• [x] symbols-view.coffee > symbols-view.js
• [x] tag-generator.coffee > tag-generator.js
• [x] tag-reader.coffee > tag-reader.js
• [x] symbols-view-spec.coffee > symbols-view-spec.js
• [x] Add devDependencies for eslint / fbjs
• [x] Add .eslintrc.js configuration
• [x] Update package dependencies to latest versions

/cc @zmb3

Translation Procedure

• Initial setup:
  • npm install -g decaffeinate
  • Install linter-eslint and enable --fix on save
  • Ensure .eslintrc.js / .eslintignore are configured correctly
• For each file:
  • decaffeinate <path to the .coffee file
  • Open .js file in atom
  • Save .js file
  • Hand edit to remove common issues:
  • Add 'use babel'; at the first line of the file
  • let > const where possible
  • Comparisons of something with null if (theThing == null) become if (!theThing)
  • Replace all instances of guard / guardFunc with plain inline ES6
  • Replace instances of function () { } with () => { } where appropriate
  • Use carriage return to make single-line statements more readable
  • Remove spurious return statements arising from implicit returns in CoffeeScript
  • Delete corresponding .coffee file

[joefitzgerald]

/cc @atom/maintainers This is ready for review. 👀

[maxbrunsfeld]

I think we can probably get rid of BaseSymbolsView, and have SymbolsView inherit directly from atom-space-pen-views. Other than that, this looks great. Thanks for the great writeup of your conversion procedure.

[joefitzgerald]

:shipit:

[maxbrunsfeld]

Thanks @joefitzgerald!