[WIP] Apply type hints across Domain app

[Benardi]

Description

Apply type hints across Domain app

Affected Dependencies

• None

Checklist

• [x] I have followed the Contribution Guidelines and Code of Conduct
• [x] I have commented my code following the OpenMined Styleguide
• [x] I have labeled this PR with the relevant Type labels
• [x] My changes are covered by tests

[IonesioJunior]

PyGrid has been moved to PySyft repository.