Actions System FR: Desired trigger conditions

The following is an off-the-top-of-my-head list of circumstances under which it might be useful to be able to trigger actions.

Ships table:
- Activation/deactivation of afterburners.
- Afterburners currently active.
- On shield quadrant depletion.
- On death. (I've looked at the death explosion mechanics enough to see that they look very limited, and I'm hoping the action system might be able to replace the retail system.)
- On 'vaporize' death.
- On non-vaporize death.

Weapons table:
- On weapon firing. (This would provide some of the functionality requested [here](https://github.com/scp-fs2open/fs2open.github.com/issues/3049).)
- On beam/projectile impact.
- On projectile detonation.
- On beam warmup.
- On beam firing.
- While in flight, while in homed flight, while in unhomed flight, while in freeflight, on ignition.