Improve readability by turning the configuration into a class

[nabla-c0d3]

Using a dictionary to store the configuration make it difficult to understand what information is stored in the configuration.

[nabla-c0d3]

As this change is going to break the API anyway, we should also rename the constructors (init VS initialize), related types and variables (such as TSKPinningPolicy) to clarify what they are as "configuration" is a bit vague.

[nabla-c0d3]

The TKSDomainPinningPolicy type is now available (added in f3aea09 ), and should be enough, for now, to clarify what's in a pinning policy.
As long as we need to support the pinning policy being set from the Info.plist file, it will need to be defined in a way that's serializable (ie. a dictionary).