RUST updates, event tweaks, shielding updates

- Merge from master. 
- RUST machinery now integrates and connects more smoothly with each other
- RUST machinery should now be buildable / researchable / orderable via cargo (medium/high requirements). 
- Shield generators/capacitors should now be buildable / researchable / orderable via cargo (medium/high requirements). 
- Tweaks to event probabilities and requirements (re-merging this commit). 
- Space carp go away at the end of the event (re-merging this commit). 
- Changelog update.