Add the beginning of a simple window manager that we'll support on Windows.

mash/wm/manifest.json

+{
+  "name": "wm",
+  "display_name": "Window Manager",
+  "interface_provider_specs": {
+    "service_manager:connector": {
+      "requires": {
+        "ui":  [ "ui:window_manager" ]
+      }
+    }
+  }
+}