Allow selecting metric from Insert Metric

It's impossible to select a metric from the "Insert Metric at Cursor" drop-down because as soon as you click on it the focus shifts to something else. This fixes that.

![srnrq](https://cloud.githubusercontent.com/assets/830952/4290557/af21900a-3dbc-11e4-8b1f-509e17afd8db.png)