Increase SessionReaper timeouts and add to config file

This should fix issues disconnecting at loading screens/zone changes as
no packets are being transmitted during this window. If the
WorldSessionsActor is also slightly overloaded, the session reaper can
drop the session mistakenly due to no outbound traffic.

Also fix-up WorldConfig.Get with better error messages along with more
tests.

common/src/main/scala/net/psforever/config/ConfigParser.scala

@@ -105,7 +105,17 @@ trait ConfigParser {
   protected val config_template : Seq[ConfigSection]
 
   // Misuse of this function can lead to run time exceptions when the types don't match
-  def Get[T : ConfigTypeRequired](key : String) : T = config_map(key).asInstanceOf[T]
+  // ClassTag is needed due to type erasure on T
+  // https://dzone.com/articles/scala-classtag-a-simple-use-case
+  def Get[T : ConfigTypeRequired](key : String)(implicit m: ClassTag[T]) : T = {
+    config_map.get(key) match {
+      case Some(value : T) => value
+      case None =>
+        throw new NoSuchElementException(s"Config key '${key}' not found")
+      case Some(value : Any) =>
+        throw new ClassCastException(s"Incorrect type T = ${m.runtimeClass.getSimpleName} passed to Get[T]: needed ${value.getClass.getSimpleName}")
+    }
+  }
 
   def Load(filename : String) : ValidationResult = {
     val ini = new org.ini4j.Ini()