Justine/refactor persisted repo

[jcocchi]

Changes:

• Deleted InMemoryRepository
• Renamed PersistedRepository to Repository
• Refactored all tests to use an in memory database with the repository
• Ensured Travis build is passing

To Test:

• All current functionality from dev should still be present
• Run all tests and make sure they pass

[kevinleung23]

@jcocchi All tests pass successfully (100 tests) and current functionality in line with dev. :shipit: