Implement abstract base models to make the base models more extendable

[diegocastrum]

also in the future converting the models to the abstract base model will make them more extendable

Originally posted by @auvipy in #46 (comment)

Adding abstract base models will make the base models more extendable in projects where extra fields are needed.

[jose-padin]

I'm working on that and I'll send the pull request with the needed changes soon.

[auvipy]

cool