Players Jobbanned from Antagonist Roles cannot be spawned as, or converted to, them

-Procs that pick from observers to make an antag will now check if they're jobbanned first.
-Converts are instead force ghosted or killed, so it's not taken as free immunity from conversion.

My thinking is that those who get jobbanned from cultist/revolutionary did something to warrant it. This could mean anything from being team-killing to working against or outright sabotaging their own team. The whole reason why jobbans are issued are to prevent players from playing roles they cannot be trusted with.  It'd be doing the revs and cultists a favor by blocking these players from conversion.

It'd be used in cases where a the jobban would be appropriate whereas a server ban could be seen as too excessive. However, the current state of these jobbans make them practically useless, as they're easily subverted by simply being converted to them, limiting corrective action to server-bans only.

Potential revs and cultists force-ghosted this way will be replaced by a suitable observer that fulfills the following criteria:
-Is not AFK
-Has the appropriate Be Antag option On
-Is not jobbanned himself

I also included a new feature with this, as a request by Cheridan.

Every time we pull a random ghost in to fill a role, we will instead poll the ghosts for volunteers first.

This means ghosts will be asked if they want to be the new blob/alien/apprentice/rev/cultist