add field in Meta WalletForm

[jucoste]

Hello,

I need to use payline with django. So I try to update your package.
Here is my first really small contribution... (maybe other will come)

• add field in Meta WalletForm (mandatory now: https://stackoverflow.com/questions/30274591/all-fields-in-modelserializer-django-rest-framework )

[magopian]

Hi, thanks for your contribution! I'm not using this library (nor am I doing any Django anymore) nowadays, so I'm not maintaining this anymore :/

Could you fork this and use it instead? I could put a link to your repository in the README, to point other people to use it ;)