Allow support for using Drill WebU through a Reverse Proxy server

Currently, Drill's WebUI has a lot of links and references going through the root of the URL.
i.e. to access the profiles listing or submitting a query, we'd need to access the following URL format:

http://localhost:8047/profiles
http://localhost:8047/query

With a reverse proxy, these pages need to be accessed by:

http://localhost:8047/x/y/z/profiles
http://localhost:8047/x/y/z/query

However, the links within these page do not include the x/y/z/ part, as a result of which the visiting those links will fail.

The WebServer should implement a mechanism that can detect this additional layer and modify the links within the webpage accordingly.