ESLint updates + linting for server.js, js/app.js, & telemetry/debug.js

[ericqweinstein]

This PR:

• Updates .eslintrc;
• Updates .eslintignore;
• Lints the following:
  • server.js
  • public/js/app.js
  • public/telemetry/debug.js

CC @yying @dguido

[ericqweinstein]

Linting goes pretty quickly—I just wanted to do this in smaller pieces to 1.) minimize the chance of regression (runs perfectly locally!) and 2.) make these PRs easier to review

[dguido]

Looks good to me!