CodeMirror JSON+Javscript Lint.
[lint addon] Start integrating

- Link to external jsonlint.js (don't want dependencies in repo if
  I can help it)

- Use a single demo file (prevent demo/ from becoming a huge mess)

- Make whitespace and newlines conform to other files, fix linter errors
WIP
[linter addon] Rewrite. Make tooltips on text work