When removing a contact, a XMPP client will not receive an explicit unavailable presence stanza for the contact from the server. Because of that Swift used to show removed contacts still with their old presence in the Chats tab or the chat view. With this patch, the PresenceOracle will flush all known presence of a contact as soon as the JID is removed from the roster. An unavailable presence will stored under the removed bare JID and is emitted via the PresenceOracle::onPresenceChange signal. Test-Information: Added a unit test verifying this behavior. Tested the behavior with two scenarios: a) Account A and B adding each other and accepting the subscription request. Starting a chat between A and B. After removing B in A's account, B used to be shown as available in the chat view and the Chats tab. With this patch B is shown as unavailable. b) Account A and B adding each other and accepting the subscription request. A removing B, and B removing A. After A adds B again, B used to be shown with the old presence even before B accepted the subscription request. This behavior is also fixed with this patch, not showing B as online until B accepted the subscription request. Change-Id: Iba97d3bedd0ac962ea00b25a0d2ed6106ed55a55