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

Use `$duration` consistently in Spinner styling

The literal value `1.4s` was used, but the existing variable `$duration` was already supposed to abstract that value.