Feature Request: UI option to open the hidden images folder

[RJWoodhead]

Since images are no longer being cleared from /tmp/ and are stored in a folder that is not simple to find and open, it would be useful to have the ability to open it from the app itself.

Also, the History tab should refresh state when the window becomes active, as images may have been deleted.

This is a little thing, so low-priority.

[mattbisme]

Opening the folder would be nice, but changing the default images folder to something like ~/Pictures/DiffusionBee would be better. Along with an option to change the default folder. And it would be nice to delete the images right from the history (#121) tab as well.