Use site-prefix for links and resources

[junkerm]

Currently, the site-prefix configuration option is only used for manually created links, for example in e-mails, but not for internal links and resources (css, images, ...).

This complicates the integration with other applications (e.g. jenkins) on a common host with a web-proxy as entry point as the proxy needs to read the HTML output and rewrite the URLs.

Obeying the site-prefix in all links in the html output produced by package-drone would help here.

For reference, see also this discussion: https://groups.google.com/forum/#!topic/package-drone/WvGQmgoHgbM

[ctron]

Closing in favor of eclipse-archived/packagedrone#47