Adds Prettier auto formatter & formats repo

[psdcode]

To avoid seeing diffs in spacing/formatting in subsequent PRs:

• Added Prettier formatter with default settings
  • Except use of single quote instead of double quote for consistency with current style
• Added scripts to package.json to run Prettier
• Added husky hook that runs Prettier on staging before a commit
• Formatted entire repo

Also:

• Added jsconfig.json to allow absolute import paths

[psdcode]

SInce formatting all files with leave my name in the git blame for all lines in these files, I will create another PR with just the formatter packages & settings & format each file I modify instead