Evaluate removing concept of default service

[davidor]

Recently we introduced the ability to remove a default service when it's the only one that a provider has (#51).

I think we should evaluate if it makes sense to remove the concept of a default service from the apisonator codebase. I believe the responsibility of deciding whether a service can be removed or not should be only in https://github.com/3scale/porta

[davidor]

The default service is important when authorizing. When a service ID is not provided in some calls, the default is assumed. That's why we can't really remove the concept of default service without breaking changes. I'll close this.