Feat/recurring v3 support

[Pelle-Jensen]

A quick and dirty update that adds V3 support(But keeps v2 support available) since june 1. marks the end of v2 deprication period
You might not want to pull it directly into 2.x as it contains a few breaking changes, and needs a bit of cleanup.

To keep compability working for v2 while migrating to v3:

• The RecurringPayments constructor now takes an api_version argument which defaults to 3 - Set this to 2
• Namespaces for: RequestCreateAgreement, CampaignRequest, RequestUpdateAgreement and Agreement must be updated from zaporylie\Vipps\Model\RecurringPayment\ to zaporylie\Vipps\Model\RecurringPayment\v2\

[zaporylie]

Hi there. First of all - it's so awesome you decided to contribute to this project. I really appreciate it.
In fact via this PR you made me aware of the June 1 deadline 🙈 I reached out to Vipps and asked them about the deadline confirmation and turns out the deadline was extended until November 1 which gives us a bit more time to make a clean transition.

I am out for 2 weeks of vacation but will have a look into the proposed PR and how to make it backward-compatible when I'm back. Meanwhile I hope extended deadline will help you with your project - I know it definitely saves me some stress ;)

[Pelle-Jensen]

Hi! Thank you, and i really appreciate the time and work you've put into this library.
It's great news that the deadline has been extended, as June 1 came as quite the shock for us as well..

No hurry with checking out the changes, have a great vacation!