Support for windows. Support for baseUrl config option.

Normalizing the path on Windows prepends C: and replaces / with \\ thus
breaking otherwise valid relative urls. This commit fixes it.
In addition, it adds support for a new config option - baseUrl.
Motivation - the static content is served by jetty running at
http://localhost:8080, but the combohandler is served by node.js at
http://localhost:8000. Before this change, such scenario was not
supported. Now it is.