add IntelliJ IDEA project related ignores

set header Content-Type "text/html"

Update to Firebase 3.x and modular Firebase builds

Update server.js

Make header prepending more elegant and simple.

Fix conding style errors (unused vars, quotes)

Use gzip compression for static assets

server-side-rendering error handling

express should not be crushed
even if server-side-rendering occurs an error.

Typo's