move all output modules to subdirectory, trash standard.nix

standard.nix isn't, is the essence here. Not all devices
support flashimage as it is currently defined - some
have diskimage, some have neither

examples/arhcive.nix

@@ -24,13 +24,18 @@ in rec {
   };
 
   imports = [
-    ../modules/standard.nix
     ../modules/wlan.nix
     ../modules/network
     ../modules/vlan
     ../modules/ssh
     ../modules/watchdog
     ../modules/mount
+
+    ../modules/outputs/tftpboot.nix
+    ../modules/outputs/kexecboot.nix
+    ../modules/outputs/flashimage.nix
+    ../modules/outputs/jffs2.nix
+    ../modules/outputs/ubifs.nix
   ];
 
   hostname = "arhcive";