Fix restarting with 32bit depth windows (v5)

What I do in this patch is:

1. Split the con_new() function, so I can create a Con without actually
create a window.
2. Store the depth of Cons in the layout file when i3 is restarting.

Fix typos and mis-staged files in previous patch.

src/ipc.c

@@ -354,6 +354,11 @@ void dump_node(yajl_gen gen, struct Con *con, bool inplace_restart) {
     }
     y(array_close);
 
+    if (inplace_restart && con->window != NULL) {
+        ystr("depth");
+        y(integer, con->depth);
+    }
+
     y(map_close);
 }