[qtcontacts-sqlite] Sort presence states by availability

The values of presence states defined by QtContacts order Busy as
more present than Away.  However, a contact who has signalled that
they are busy is likely to be less available for communication than
one who has Away status. Add (and enable) an option to reverse the
ordering of these two states.
Merge pull request #97 from matthewvogt/presence-order

[qtcontacts-sqlite] Sort presence states by availability