Allow loading of URIs from classpath

When passing configuration_uri in properties, we should provide a way to load resources from the classpath.
Since the JDK doesn't have a comfortable URL handler for classpath, we should do the following:

• if the URI is relative (i.e. it doesn't provide a protocol), attempt to load the resource from the system classloader and TCCL.
• provide a URLStreamHandlerFactory which handles the classpath: protocol