Add primary key constructors
Make playground - config bidirectional relashionship, add unique
constraint
Use different approach on updating game results
Make GAV comparable
Fix unique constraint on PlaygroundConfigEntity
Move from injected fields to injected constructors

Injected constructors allow far easier testing using the mock
implementations of real objects.
Add a logic layer between data and services/ui layers

This way no logic is present in REST services that are now purely a
presentation layer. The logic layer can be later on used by UI to get
the same results as the REST clients.