Consider adding a field with an image used for preview

[0pdd]

The puzzle 1282-0969f19a from #1282 has to be resolved:

mystamps/src/main/resources/sql/series_dao_queries.properties

Line 161 in d953dbf

# @todo #1282 Consider adding a field with an image used for preview

The puzzle was created by Slava Semushin on 30-May-20.

[php-coder]

We can add a dedicated field into series table. Another option is to try to optimize the SQL query by JOIN-ing with a temporary table that is created from series_images.