Investigate and create API definition model

[ldmi3i]

Investigation required here.
You need to analyse swagger file structure and create API definition model based on structure.

[ldmi3i]

Added the initial Api Specification document model.
For the initial version I propose to do some simplifications sacrificing some data duplication.
The Open API specs have something like library of predefined components to use in repetitive parts of models.
I'm proposing to do this generealisation later. (also it's usually about response models that we don't need at all).
#7

Please check it - do you agree with such model?