Execution animations for bossfights#649

When the boss is at a very low amount of health, you can press a hotkey to execute them, which would trigger an animation of your MASS doing something like hook-punch them while boosting upwards or fire missiles at them in a more cinematic camera angle.

Animating an execution for every weapon type would be too much, so relying on tools that every MASS would have is probably the best way to do it.

Suggested already in post #273 (enemy executions). Merging posts.