Remove magerun dependency

[bobbyshaw]

We built magedbm on top of Magerun for speed of development. To reduce dependencies we could re-implement the small portion of magerun that we use:

• Find magento application root
• Reading app/etc/local.xml file to get database credentials.
• Database dump with mysql exec (we've already integrated a PHP alternative when exec isn't available.

[bobbyshaw]

This is a low priority.

[punkstar]

The first two bullet points could be achieved with https://github.com/meanbee/libmageconf these days.