Specify tag order in spritesheet export

[mbasaglia]

I'd like to have some option to specify the order of frame tags when exporting a spritesheet.
Currently they seem to be in creation order (first tag you create is the first exported) but it would be useful to have some flexibility on that.
If you want a specific order with the current behaviour you need to fiddle a lot with the tags so it would be quite helpful to have some kind of easy to understand ordering.
Ideally you'd be able to manually set the export order but also just exporting them based on the frame number would also be a good solution.

The main use case for me is when editing a spritesheet that is already being loaded from somewhere should keep frames in the same position so you don't need to update all the frame offsets when you change your frame tags.