Disable save/load script to disk when appropriate

In the script editor, "Save to Disk" and "Load from Disk" should be disabled when you don't have copy and/or modify permissions. (I.e. when the script contents are hidden / non-editable.)

This is just a UI cue, not a content theft issue. If you save the script now, it saves the "You are not allowed to view this script." message instead, so no harm done.