Refactoring the return logic for toDos

[aasheptunov]

Refactoring the return logic for toDos.

User story:
As a developer, I want the GET /to-dos endpoint to return only uncompleted tasks, so that the UI only receives current tasks when accessing the endpoint.

DoD:

• When a GET request is sent to the endpoint /to-dos, the server returns an array of uncompleted tasks.
• A GET endpoint for /to-dos/complete has been added, which returns an array of completed tasks.