Add a VVV specific configuration for phpMyAdmin

Allows us to specify that dropping databases is ok. This would normally be an undesirable thing, but our requirements are a bit different when running it locally in a VM.

This also sets us up to configure phpMyAdmin in other ways.

Closes #216
Merge pull request #218 from 10up/216-enable-drop-database

Add a VVV specific configuration for phpMyAdmin