mount_server: Ported to a launch_daemon world.

* Now inherits from BServer, and gets its message port from the
  launch_daemon.
* It registers an event "initial_volumes_mounted" that allows other
  services to be started afterwards.
* This is now used in the boot launch files, and makes the scripting
  based previous solution superfluous which has been removed with this
  commit, too.
* This implements the last needed feature in order to reproduce the
  complete former boot process using the launch_daemon.

data/launch/system

@@ -26,7 +26,6 @@ service x-vnd.Haiku-SystemLogger {
 
 service x-vnd.Haiku-mount_server {
 	launch /system/servers/mount_server
-	legacy
 }
 
 service x-vnd.Haiku-media_server {

data/launch/user

@@ -4,11 +4,17 @@ target desktop {
 	service x-vnd.Be-TRAK {
 		launch /system/Tracker
 		legacy
+		on {
+			initial_volumes_mounted
+		}
 	}
 
 	service x-vnd.Be-TSKB {
 		launch /system/Deskbar
 		legacy
+		on {
+			initial_volumes_mounted
+		}
 	}
 
 	job create-installer-link {