Specify skeletons for JSON or binary export

[misaki-eymard]

Currently, you can manage whether a skeleton is exported in JSON or binary format by checking or unchecking the Export option for each skeleton, but in cases where a large number of skeletons are included in a single Spine project, it may be convenient to be able to select the skeletons to be exported in the Export window, or to specify which skeletons to export via the CLI. (This probably takes precedence over the Export option for each skeleton.)

Related forum thread:
https://esotericsoftware.com/forum/d/26465-spine-cli-export-option-for-specific-skeleton/17