HTTP file server

Initial implementation for serving static content from RxNetty based on https://github.com/netty/netty/blob/master/example/src/main/java/io/netty/example/http/file/HttpStaticFileServerHandler.java.  

Additional features include,
1.  Support for single and multiple file sources
2.  zero-copy serving of files

There is a security issue here, there is nothing to prevent the caller from navigating the filesystem.  This may also exist for the classpath, but I am having a harder time proving that.

```
val uri2 = new URI(s"file:///$prefix/../../etc/hosts")
uri2: java.net.URI = file:////Users/gorzell/../../etc/hosts

scala> import java.io.File
import java.io.File

scala> new File(uri2).exists
res10: Boolean = true
```