Add: deity mode enforcement checks to functions with command or company access

Command functions are those that call ScriptObject::Command, and functions
with company access are any that call ScriptObject::GetCompany. This is a bit
over-protective, but having the check everywhere makes it easier to validate
that no check is missing automatically instead of by review.

src/script/api/script_subsidy.hpp

@@ -55,6 +55,7 @@ public:
 	 * @param to_type The type of the subsidy on the 'to' side.
 	 * @param to_id The ID of the 'to' side.
 	 * @return True if the action succeeded.
+	 * @pre ScriptCompanyMode::IsDeity().
 	 * @pre ScriptCargo::IsValidCargo(cargo_type)
 	 * @pre from_type == SPT_INDUSTRY || from_type == SPT_TOWN.
 	 * @pre to_type   == SPT_INDUSTRY || to_type   == SPT_TOWN.