Update category.php

Improved Categories Menu;
a) 1 DB call for All Categories (rather than 1 for root cats + 1 per cat for children).
b) 1 DB call for Product Counts (rather than 1 per category).
c) Unlimited levels (no more Parent+Child only!).

ToDo;
1) will introduce a MaxLevel option
2) will refactor so ProdCount is standard for NoStubs - but visible output is optional (hide 0's as well!)