[qtcontacts-sqlite] Switch to user_version for schema management

Sqlite now supports the user_version pragma, which provides a more
flexible mechanism for managing database versioning.
[qtcontacts-sqlite] Index the likely filter columns on Contacts table

The status columns are likely to be used to filter queries over the
primary table.
Merge pull request #103 from matthewvogt/user-version

[qtcontacts-sqlite] Index the likely filter columns on Contacts table