Improve performance of megamenu to reduce the response time on first-time login

[jmiranda]

This pertains only to locations with thousands of shipments. Should be able to go from 10 seconds to under 1 second with a little reworking. The issue before was that we were always calculating the current status in memory since we weren't keeping track of current status in the database. We added a current status field to shipment a few release back, so we should take advantage of that and delegate the "shipment count by status" query to the database.