Standardize `createId()`, use last modified time by petebankhead · Pull Request #2013 · qupath/qupath

@petebankhead

Fixes https://forum.image.sc/t/bioformats-importer-issue/25439/2

Opening an image in QuPath after it has been modified should no longer result in tiles being returned from the cache - at least for OpenSide, ImageJ and Bio-Formats.

Other ImageServer implementations are responsible for creating their own ID that encodes this information, or using the new `ServerTools.createDefaultID` method.