Add a windows signing script

As electron builder doesn't support supplying a key container name
which is the only way we can supply the token passphrase

package.json

@@ -97,11 +97,12 @@
     "win": {
       "target": {
         "target": "squirrel"
-      }
+      },
+      "sign": "scripts/electron_winSign"
     },
     "directories": {
       "output": "dist"
     },
-    "afterSign": "scripts/electron_afterSign.js"
+    "afterSign": "scripts/electron_afterSign"
   }
 }