v0.13 separate Claim and Claims classes into own files

[dpriskorn]

I prefer not to have more than one class in each file to ease navigation.

[LeMyst]

It was a choice at the beginning because the classes were small, but now it's a good idea to give each class is own file.

[LeMyst]

Spliting the files create a lot of circular import, and I don't really understand why.