* change version checks to `which` instead. add comments around imvr in linux

* add which checks for renamer and preview-tui as well

* nuke: use macOS open when GUI enabled

* nuke: use is_mac function to test for macOS

This is consistent with how the imgur plugin does detection.

* Add macOS open command to plugins

* pskill: only execute if input is non-empty

* added support webp format

* update nuke plugin with support webp format