Implement: TestContacts for consumer UI testing

[vestrel00]

This library should implement TestContacts, which consumers can use as a substitute to their Contacts API instance in black box tests; UI instrumentation tests in androidTest/.

Consumers should also be able to use this in their production apps, not just in tests. If they want their production app to interact (query, insert, update, delete) with only "test contacts", all they should need to do is substitute their Contacts API instance with an instance of TestContacts.

Howto guide is at #45