Add support for time-limited actor upgrades.

This adds support for limited-time upgrades, and adds a warheads and support power upgrade source.

These changes are demonstrated by porting the Iron Curtain to use upgrades, adding an invulnerability crate to RA, and implementing the plumbing for EMP in TS (but doesn't attempt to fix the other limitations).
This will NRE if the actor doesn't have `UpgradeManager`.