Re-add company shares

src/settings_type.h

@@ -658,6 +658,8 @@ struct EconomySettings {
 	bool   inflation_fixed_dates;            ///< whether inflation is applied between fixed dates
 	bool   bribe;                            ///< enable bribing the local authority
 	EconomyType type;                        ///< economy type (original/smooth/frozen)
+	bool   allow_shares;                     ///< allow the buying/selling of shares
+	uint8  min_years_for_shares;             ///< minimum age of a company for it to trade shares
 	uint8  feeder_payment_share;             ///< percentage of leg payment to virtually pay in feeder systems
 	byte   dist_local_authority;             ///< distance for town local authority, default 20
 	bool   exclusive_rights;                 ///< allow buying exclusive rights