Added Entity and ListEntity support for Zend Db

*NOTE* This is very ugly at the present moment and without changes to Contain itself it will be hard to optimize this.  I thought about adding it as a new property mapping but that seems to be more clutter.

Take a look at the PR; it works for both Entity and ListEntity now by doing subselects.  Later on it might be better to turn these into 1:1 or 1:m but for now this was the best and easiest method of adding this in.