Implements existing assistant alternate job titles

Adds an option to choose one of the alternate job titles for assistant
already defined at
https://github.com/Baystation12/Baystation12/blob/master/code/game/jobs/job/assistant.dm#L12

code/modules/client/preferences.dm

@@ -507,6 +507,8 @@ datum/preferences
 				HTML += " <font color=green>\[Yes]</font>"
 			else
 				HTML += " <font color=red>\[No]</font>"
+			if(job.alt_titles) //Blatantly cloned from a few lines down.
+				HTML += "</a></td></tr><tr bgcolor='[lastJob.selection_color]'><td width='60%' align='center'><a>&nbsp</a></td><td><a href=\"byond://?src=\ref[user];preference=job;task=alt_title;job=\ref[job]\">\[[GetPlayerAltTitle(job)]\]</a></td></tr>"
 			HTML += "</a></td></tr>"
 			continue