implement zwlr_foreign_toplevel_management protocol (#452)

* implement zwlr_foreign_toplevel_management protocol

* check if initial id is empty

wire/zwlr_foreign_toplevel_manager_v1.txt

@@ -0,0 +1,15 @@
+# requests
+
+request stop {
+
+}
+
+# events
+
+event toplevel {
+    toplevel: id(zwlr_foreign_toplevel_handle_v1)
+}
+
+event finished {
+
+}