Possibility to access res.locals variable across all views

[yaneony]

See #207.
Is test still necessary for one-liner?

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[Eomm]

Is test still necessary for one-liner?

Yes, you could just transform the code in the issue to a test that should fail before your changes, and pass after it.

This will assure your fix will be preserved overtime

[yaneony]

Test added and passed.

[mcollina]

lgtm