Create an `api` package to handle backend responses

[amaury1093]

Create a @chronoscio/api package, where we:

• manage the axios requests in one place
• create TS interfaces for all our models
• add validations for these models

So that basically we have: backend ---send json--->@chronoscio/api, who processes and normalizes data ---sends normalized, typed data ---> rest of app

cc @whirish let's do this after we merge your PR.

[quorth0n]

Closed via #24