Add Monga adaptor

[emlynwest]

Add an adaptor so an instance of monga can be used for the DBAL.

https://github.com/FrenkyNet/Monga

[sagikazarmark]

IIRC Monga has been moved under the league and @FrenkyNet does not maintain it anymore.

[emlynwest]

Indeed you are correct https://github.com/thephpleague/monga