Server build date and revision.

Can now see the current compilation date and revision:
* In the Dream Daemon log output.
* By using the "Show Server Revision" client verb which also links you to the commit in question.

code/controllers/configuration.dm

@@ -90,6 +90,7 @@
 	var/banappeals
 	var/wikiurl
 	var/forumurl
+	var/githuburl
 
 	//Alert level description
 	var/alert_desc_green = "All threats to the station have passed. Security may not have weapons visible, privacy laws are once again fully enforced."
@@ -376,6 +377,9 @@
 				if ("forumurl")
 					config.forumurl = value
 
+				if ("githuburl")
+					config.githuburl = value
+
 				if ("guest_jobban")
 					config.guest_jobban = 1