Use old id for "Peek at Desktop" to preserve existing shortcus

This code uses the DEF() macro which silently re-uses an untranslated
version of the string as the ID in the config file. So anytime you
change the text, a new entry will be created in the config flil and
users will lose any custom shortcut mappings.

To avoid this, use the DEF2() macro instead, which allows defining the
ID and the user-facing translated name differently.