SmallTalk. API prototype. DataLayer 

(DataLayer):

- [ ]   Include EntityFramework
- [ ]   Implement a DataContext
- [ ]   Add Entities of DataContext
- [ ]   Implement a Mappings (Model -> Entity, Entity to Model, IReadOnlyCollection)

[AB#41](https://dev.azure.com/o2-bionics-llc/cda9516b-08ff-4491-bc59-836494579e0d/_workitems/edit/41)

AB#224