Added file output suffix functionality

[crtgregoric]

No description provided.

[skjorn]

Hi, thank you very much for your addition! I modified the layout of the dialog a bit and fixed the space to be added before the suffix, not after. Would you be so kind to check my modifications (files attached below) against your submitted version, apply them and re-submit your pull request again? I'll be happy to merge it. (Sorry, had to rename the files to .txt for GitHub to accept them.)

dialog.json.txt
Export Layers To Files (Fast).jsx.txt

[crtgregoric]

I have reviewed your changes and looks good to me.
The new layout is much better.
As for the spaces, in my testing no spaces were added (which suits my needs), so not really sure what should it do (should the output file be named "{prefix} name {suffix}"?).

[skjorn]

Basically, it adds the spaces (as you mentioned it becomes "{prefix} name {suffix}") and then converts them to '_' if "Allow spaces" is not set, so this should be fine.

Thanks, I'll merge it then.