Admin widgets - add remaining widgets.

Adds column 1 - new customers and counter history
Adds column 2 - new orders
Fixes bugs in dashboard widgets with 0 rows (initially counter had 0 rows).
Fixes bugs in counter logic (made counter work)

This was merged in to Zen Cart 1.6 in the following update:
https://github.com/zencart/zc-v1-series/blob/5a2f19ae8c07b7490bbbc9c204dd0bdcae46d35f/zc_install/sql/updates/mysql_upgrade_zencart_160.sql