WebServer Headers for Request are treated case-insensitive

To achieve this, Request Headers are stored in both "original" and "lowercase".
In this way we don't mangle with the request object we have received, while
still be able to handle headers when NOT in the classic "Camel-Case" format.

Fixes #11421.
Merge pull request #11422 from detro/ghostdriver-dev

WebServer Headers for Request are treated case-insensitive