Allow RA to return slaves to previous assignment

Description and notes

Allow RA to return slaves to their previous assignments(if possible/safe)

Merge Checklist

• I have read CONTRIBUTING.md
  • and
    • my code editor has
      • ESLint support enabled
      • TypeScript support enabled
      • some form of spell checker
        • We suggest using a spell checker compatible with cSpell if possible
    • my changes compile successfully and seem to work properly
    • I am using the simple compiler (simple-compiler.[bat or sh])
    • I am using the normal compiler (compile.[bat or sh])
    • this is my first merge request
    • the changes in this merge request comply with the coding style defined in CONTRIBUTING.md

Changes made

• Add new option to "Automatically set assignment" RA option
• handle new option in ProcessAssignments

Things left to do

• code review (this is done by one or more people other than you)
• final tests
• let Pregmodder know that this is ready for merging