Change: Allow AI companies to start immediately.

Allow multiple AIs to possibly start in the same tick.
start_date = 0 becomes a special case, where random deviation does not occur.
If start_date was not already 0, then a minimum value of 1 must apply.

src/script/script_config.hpp

@@ -139,7 +139,7 @@ public:
 	/**
 	 * Randomize all settings the Script requested to be randomized.
 	 */
-	void AddRandomDeviation();
+	virtual void AddRandomDeviation();
 
 	/**
 	 * Is this config attached to an Script? In other words, is there a Script