Scala: tentatively add SemanticURIGuesser.scala to classify URI as semantic or various kinds of "non-semantic"

TODO: crashes:
[info]   java.lang.NoSuchMethodError: akka.actor.Props$.apply(Lscala/Function0;Lscala/reflect/ClassTag;)Lakka/actor/Props;
[info]   at spray.can.HttpExt.<init>(Http.scala:153)