Allow user to skip, edit script in place, or abort on preset custom script failure

[jamesmcm]

Task

If a custom script in a preset file fails we should ask the user if they want to either:

• Skip the script and continue with the rest of the presets
• Edit the script (i.e. edit the tempfile in the host's $EDITOR) and re-run it after modifications
• Abort ALMA execution entirely (the current behaviour)

Justification

This will make it easier for users when composing a system with many preset files (i.e. you don't want to re-install 100 packages again because of a typo in one preset script).