Refactor DatabaseListGenerators

[DrBarnabus]

Refactor DatabaseListGenerators to use a single generic interface, as a significant portion of their code is generic we can then reuse it to reduce the amount of code reuse in the application.

Making both use a generic interface will mean adding some kind of method to detect if the generator is the current active generator; Blacklist or Whitelist. Although it would make it easier in the future if an ability was added to make your own Database List Generator extending IDatabaseListGenerator.

[DrBarnabus]

Looking back on this now, not a whole lot of the code is duplicated so I think the current way it works is nicer.

Closing this issue for now.