Add the ability to get resources from JAR archives

[nartamonov]

Currently Http.fromResource is able to provide file resources only. However, it is often necessary to provide a resource that is inside a JAR archive. For example, if you run an application through sbt run, the application classes and resources will be packaged into a temporary JAR archive, and the resource URLs will have a jar:file scheme. Now such resources cannot be obtained with Http.fromResource. This PR adds this feature. Based on the implementation of ResourceFile from akka-http.