AI: many AI tweaks

- Optional, requires cheat cvar:
- Marine bots unweld doors marked by the mapper as fit for that purpose
without being requested to.
- Marine bots hack terminals without being requested to if the squad
leader is a bot.
- Marine bots call for a medic if they think they will die in the next
hit.
- Marine bots can melee when being mobbed by aliens.
- Marine bots shoot at shieldbugs' brains instead of their middles.
- Always on:
- Marine bots can shoot eggs
- Marines and aliens avoid routes through areas where their allies have
died recently.
- Marines and aliens avoid fire.
- Buzzers use navmeshes.
- Non-jumping drones no longer jump unless there is no other option.