Check whether Sqlite is compiled with SQLITE_ENABLE_UNLOCK_NOTIFY

The QSQLITE3 driver now requires that SQLite is compiled with
SQLITE_ENABLE_UNLOCK_NOTIFY, which enables the unlock_notify API.

It turns out that some distributions ship SQlite compiled without
this option and Akonadi then fails to compile.

To prevent this, we detect whether SQlite is compiled with unlock_notify
API at configuration time by compiling a simple check in FindSqlite.cmake.