Implement ResourceCache

[Citymonstret]

//
// This is going to download a resource from an external server and store
// it on the current server. All resources served by the resource cache
// are going to have all the required cache headers.
//
final ResourceCache resourceCache = new ResourceCache("assets");
resourceCache.addResource("https://code.jquery.com/jquery-3.3.1.min.js");
resourceCache.create();