Add Kasboeking and Dagboek functionality

[ikulis]

Dagboek [findAll]
Kasboeking [find/add/update/delete]

Made mode specific class SnelstartPHP\Model\V2\Koopboeking which is extended by Verkoopboeking and Inkoopboeking, so I can extend the base SnelstartPHP\Model\V2\Boeking.

[manuelderuiter]

Thanks for your contribution! It looks great so far. Haven't had the opportunity to test it yet.

[arwinvdv]

@ikulis to add a Kasboeking, the inkoopboekingBoekingsRegels and verkoopboekingBoekingsRegels params has to have an boekingId. I fixed it in 2119add

edit: typo

[ikulis]

@arwinvdv Indeed overlooked it, I was testing with the grootboekBoekingsRegels. Thank you for testing that one. Are you able to attach to the pr or should I do it?

[arwinvdv]

I'm not that experienced with pull requests so it would be nice if you can do that.