Search dashboard dropdown doesn't work well with a large number of dashboards

The search dashboard selector dropdown doesn't work well when there is a large number of dashboards because it pushes the "view all dashboards" and "view all indexes" past the bottom of the page. It doesn't support scrolling either, so either you need to zoom the page out or manually construct a url to get to a specific dashboard/index. We should probably limit the number of dashboards or add scrolling to the widget.