Cleanup

- Replaced 'EXP' with "Playtime' in most admin-visible locations. The
system is still invisible to normal players.
- Changed the types of exp you can accumulate from 'all', 'eng', 'sup',
etc to more human-friendly names like 'Crew', 'Engineering', and
'Supply'.
- Eliminated some copy-paste.
- Added a new configuration option: use_exp_restrictions_heads_hours.
When enabled and set to a >0 value, it overrides all head/ai job
playtime requirements, instead substituting that number of hours.

code/modules/admin/admin_verbs.dm

@@ -75,7 +75,7 @@ var/list/admin_verbs_admin = list(
 	/client/proc/debug_variables,
 	/client/proc/show_snpc_verbs,
 	/client/proc/reset_all_tcs,			/*resets all telecomms scripts*/
-	/client/proc/cmd_admin_check_player_exp
+	/client/proc/cmd_admin_check_player_exp /* shows players by playtime */
 )
 var/list/admin_verbs_ban = list(
 	/client/proc/unban_panel,