added support for http basic auth in JVM URL

## Basic Auth

When securing jolokia using http basic auth, the current implementation does not pass the credentials from the JVM url down to `jolokia.js`. For example, using `http://user:pass@example.com/jolokia/` as the JVM URL will fail, as every ajax request will be send without authentication headers.

## Proxies

Additionally when running jolokia behind some proxy like nginx, the basic auth will fail due to  the `jolokia.js` library not setting the `Authentication` header and relying on jquerys on-demand authentication, which is not supported by all servers.

See https://github.com/rhuss/jolokia/pull/98 for details.