Create PsAdmin framework

PsAdmin uses a dedicated TCP port to allow for remote queries and
command to be sent to the running World/Login server. Commands are a
single command followed by zero or more arguments.

Commands may require access to the ActorSystem, so they will get their
own dedicated actors to be able to handle the different messages
required that can be sent in response to a query. The return line is in
JSON to allow for easy parsing by applications, such as web servers.
An interactive client is easy as being able to parse json and buffer
command input.

Some basic commands are implemented for now:

* shutdown - kills the actor system
* list_players - gets a list of players on the interstellar cluster
* dump_config - get the running config
* thread_dump - dumps all thread backtraces (useful for prod debugging)

More advanced commands like kick/ban will require additional testing.

build.sbt

@@ -46,9 +46,9 @@ lazy val commonSettings = Seq(
     "org.ini4j"                  % "ini4j"         % "0.5.4",
     "org.scala-graph"            %% "graph-core"    % "1.12.5",
     "io.kamon"                   %% "kamon-bundle" % "2.1.0",
-    "io.kamon"                   %% "kamon-apm-reporter" % "2.1.0"
+    "io.kamon"                   %% "kamon-apm-reporter" % "2.1.0",
+    "org.json4s"                 %% "json4s-native" % "3.6.8",
   ),
-  classLoaderLayeringStrategy := ClassLoaderLayeringStrategy.Flat
 )
 
 lazy val pscryptoSettings = Seq(