Remove triggers from Sqlite implementation

[HannaLindgren]

It seems as if the Sqlite triggers do not work properly (at least not the one for prefererred tags).

We need to remove triggers and add code instead to do these tasks (look for solutions in the MariaDB version, since triggers never worked there).

Triggers to check:

• preferred tags (only one preferred)
• entry status (only one current)
• entry tag