Create Tasks database model, DAO and API list method

[isabelcosta]

Description

As a developer,
I need to create Task database model,
so that I can start creating the APIs.

Anyone in the current mentorship relation, mentor or mentee, can create, delete tasks and mark them as achievements.

Acceptance Criteria

Update

• Create the database model
• Create tests for the database model
• Create DAO list function
• Create tests for the DAO function
• Create API to list tasks
• Create tests for API list endpoint

Definition of Done

• All of the required items are completed.
• PR should be sent to the gsoc18-code branch
• Approval by 1 mentor.

Estimation

4 hours