indexer: better way to find wheels

[francisdb]

Maybe some strategies that go from very strict to less strict

• a exact [tablename]-wheel.png
• a wheel.png next to the table
• any png next to the table containing wheel
• any png in subdirectories containing wheel

Preferably something that also works without the requirement to have a folder per table?

also JPs Space Cadet (GE)V1-1.vpx and JPs Space Cadet (GE)V1-1-wheel.png currently does not work.