Feature: Mission Randomization (Type Swaps)

[dreamsyntax]

• Initial version will only shuffle mission types, not implement new custom object missions
• Compute valid/possible missions only
• For chase missions, needs to either utilize existing splines or generate new ones. We also need to add chase objects to the HPP definitions. They are hardcoded in 0210, 0501, 0502 - but can be manually placed as setobjs.