Fixes for the MSI installer (#3043)

* Run uninstaller for EXE synchronously so that it doesn't try to uninstall while also installing

* Display error message before running MSI installer to close the application manually

electron-builder.json

@@ -180,6 +180,9 @@
     "uninstallDisplayName": "${productName}",
     "include": "scripts/installer.nsh"
   },
+  "msi": {
+    "additionalWixArgs": ["-ext", "WixUtilExtension"]
+  },
   "rpm": {
     "fpm": ["--rpm-rpmbuild-define", "_build_id_links none"]
   }