Incorrect routing when using a nested URL with routePrefix

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When setting a nested URL through another web server (per best practice) litecore node is incorrectly setting the route URL as root while building the route prefix, see below:

https://github.com/litecoin-project/litecore-node/blob/be0cd40ef806dfdf020d2918e3fab80f022e135b/lib/services/web.js#L106

This will break any complex setup where a reverse proxy or firewall is set infront of litecore node.

The patch should take into account the possibility of a nested URL when building the prefix. I don't have a PR for this right now but a rough hot patch for existing services would look something like:

this.app.use('/deep/nested/' + this.node.services[key].getRoutePrefix(), subApp);