WIP - TK Proxy fixes - REVIEW ONLY

For now, this is a review-only PR showing what changes are required for the pe-trapperkeeper-proxy.

- This PR
- bumps schema version to support the Bool type (needed in dependent projects)
- moves jetty version to a variable to enable easy jetty version change
- bumps version of the http client
- enables using the latest jetty client (a workaround with the Logger creation is needed)
- adds another hook in the add-proxy-route which enables changing the URI early enough in case of redirection (AFAIK request in the callback-fn cannot change its hostname), if we say that we'll always redirect within the same hostname then we can try to merge this hook into the callback-fn as well
- adds support for authorization via the 'authorize-fn' callback function which can either grant access to the target URI, or send a redirect to a different URI (typically the "forbidden" page)

Note: The documentation is not updated (regarding the add-proxy-route) since this is just a proposal of adding yet another callback function and I am not sure if it's acceptable. If not then we can try to live with the original callback-fn only but we'll be limited in actions that can be done if user is not authorized to visit the target URL. Ideas are welcome!

I totally agree, I have reorganized a lot of my code, and in the final implementation I wouldn't actually need this hook at all. However, in such a case, I would need adding more features to the webserver service which I call "middleware support" (my initial proposal, without any tests written, is here https://github.com/fhrbek/trapperkeeper-webserver-jetty9/compare/wip_middleware_support?expand=1). I'm afraid it's too late for adding such a thing now, so I think I will suggest adding the "rewrite-uri-callback-fn" for now.