Use XEP-0012: Last Activity

[daniele-athome]

Drop use of roster presence last seen information (which would be sent by the server everytime even if it's not used by clients) and replace it with a last activity request sent on every opening of the compose message fragment. This guarantees live retrieval of the last seen value and lighter roster presence information at the expense of network traffic and energy by the client - this is also an opportunity to test the connection to the server.

Be sure to cache the value into the Contact instance to avoid making a request every time.