Space Ninja Gamemode Implementation

Changes:
* Enabled continuous_rounds: One-antag rounds (like wizard/ninja) no longer end automatically upon death
* Space ninja has been implemented as a voteable gamemode
* Space ninja spawn landmarks are in the code, but have not yet been placed on the map. They spawn at carpspawns instead.
* Five new space ninja directives have been added, old directives have been reworded to be less harsh
* Space ninjas have been given their own list as antagonists, and are no longer bundled up with traitors on the Check Antags panel
* Space ninjas with a "steal a functional AI" objective will now succeed by downloading one into their suits
* Space ninja suits' exploding on death has been nerfed, so as not to cause breaches, as this was OP and could only be metagamed
* A few space ninja titles/names have been added and removed to be slightly more believable
* The antagonist selector no longer chooses jobbanned players when it runs out of willing options (this is slightly unrelated but it seemed unnecessary)

I still have more changes/tweaks in mind, just wanted to get this up here so other folks can begin contributing what they want to, and get an idea how well the mode works before a lot of overhaul. I've tested what I can, BEF will have to do the rest.

Please let me know if there's anything that could be improved in the code, a lot of it was copypasted.