[WIP] Use PasswordInterface instead of Bcrypt

I have a legacy API which does not use the bcrypt for password encryption. In order to not require users to change passwords I would like to configure which implementation of `PasswordInterface` this module uses.

This PR relies on the release of my [ZF2 PR](https://github.com/zendframework/zf2/pull/6447) which adds the `PasswordAwareInterface` 

This PR is still very much a work in progress, but any feed back I can get would be greatly appreciated.

I still need to figure out the best pattern for configuring the PasswordInterface implementation.