Add InMemoryVersionedBackend

[furkilic]

Hello

Quick PR to be able to do some Versioning (only for InMemory usage) by simply enabling the InMemoryVersionedBackend like this :
S3Mock api = new S3Mock.Builder().withPort(8001).withInMemoryVersionedBackend().build();

InMemoryVersionedProvider was really close to InMemoryProvider so AbstractInMemoryProvider was added for abstraction
Also written some test cases

It's my first time doing Scala so do not hesitate to share your input.

I really appreciate this project really helpfull in for tests, however versioning will be a big plus for us as it's really needed in my current project.

Thanks in advance

furkilic

Linked to #155

[furkilic]

Hi @shuttie @romangrebennikov

Is it possible to have a feedback please?

Thanks in advance

[ghost]

Would love to see this merged

[ifs-medardegue]

Definitely need this.