Align default Thumbnail resolutions with our clients' requirements

## Describe the bug

Currently we have this for the allowed thumbnail resolutions in the thumbnails service:

`{"16x16", "32x32", "64x64", "128x128", "1080x1920", "1920x1080", "2160x3840", "3840x2160", "4320x7680", "7680x4320"}`

AFAIK this doesn't really align with what the clients (web mainly, didn't check others yet) actually need.

For the the grid view web would benefit from a size between 128x128 and 1080x1920. Currently it seems to request a 1000x1000 thumbnail (of type `fit`). If I understood @kulmann correctly, it does so because if it requested a more reasonable size the thumbnailers "ClosestMatch" check would fall down to 128x128 which is too small for the grid view.

Also I think we should get rid of the huge 4k and 8k thumbnails in the default config. Who needs that in the preview app? If somebody really needs that, it can always be configured with `THUMBNAILS_RESOLUTIONS` manually.

Also I am not sure if we really need 16x16 in the default config.

@kulmann Can you come up with a list of thumbnail dimension that would be useful for web (for the list view, the grid view and the preview app ideally).