Change behaviour of some image properties
Function to build image query string

Database views would be a much better idea than to puzzle out
complex queries in PHP. Unfortunately MySQL/MariaDB 5.5 cannot
efficiently merge views with a GROUP BY clause into new queries.
Instead it uses temporary tables, which are awfully slow.
Add constructor behaviour to Image class

The PDO "class" fetch mode doesn't invoke setters. Therefore pass hints
to the constructor to invoke them afterwards.
Use query builder to fetch images
Display tags again in image view