Implement Staged fallback system for mission generation

[john681611]

• [x] Determine top level Stages
• [x] Create commit/staging method
• [x] Create basic roll back logic
• [x] Create rollback logic for each stage
• [x] Migrate State from UnitMaker to mission
• [x] Migrate State from SpawnpointSelector to mission
• [x] Migrate State from DrawingMaker to mission
• [x] Migrate State from ZoneMaker to mission
• [x] Check and migrate all remaining states to Mission (refactor mission to minimise the horror of this)
• [x] Fix MapData Double Entry bug (likely hiding something else nasty)