Add QSQLITE_OPEN_URI database connection flag

This flag enables the URI mode for database names in the SQLite
backend. Without this flag, it's not possible to use URIs like
    'file:somedb?mode=memory&cache=shared'
to create shared, in-memory databases.

Change-Id: I2938184dad1f27c7af454385ca305bd4f6ed1a5e
Reviewed-by: Mark Brand <mabrand@mabrand.nl>