add sequelize backend

[tbarbugli]

[tbarbugli]

@tschellenbach @nparsons08 do you guys have any code example to share about this? Even something generic and not yet specific to sequelize would be nice

[tschellenbach]

https://github.com/sequelize/sequelize

should be pretty similar to our support for Waterline. Did anybody ask for this?

[solon]

@tschellenbach @tbarbugli a Sequelize example would be helpful for @colinramsay and I

[dwightgunning]

I have a little bit of experience with Sequelize but don't have time for this right now. It could also a nice community contribution if somebody would like to submit a PR.

[agustif]

@dwightgunning Could you at least provide some gguidance on how would one go about adding more 3rd-party backend orm support.

+1 for Sequelize but I would like to try myself for FaunaDB and TypeORM.