Select an icon for each action button

The action button of each script, which is a media play icon by default, should be assignable by the user.

Steps to select an icon:
1) Click the browse button near the action button for that script.
2) A file picker or browser will show, and the user will pick a picture file to use.

Result:
1) The action button for that script will show the selected icon instead of a media play button.
2) The file browser should remember the directory of the last selected icon. The next time a browse button is clicked the file picker will start in the last-known directory.