Add support for inherited test suites

[philippleidig]

Add support for inherited test suites derived by a common base function block extending the TcUnit.FB_TestSuite.

TMC sample:

<DataType>
	<Name>MyUnitTestSuite</Name>
	<ExtendsType Namespace="TcUnit">FB_TestSuite</ExtendsType>
	<Method> ... test cases ... </Method>
	<Properties></Properties>
</DataType>
<DataType>
	<Name>MyDerivedUnitTestSuite</Name>
	<ExtendsType>MyUnitTestSuite</ExtendsType>
        <Method> ... test cases ... </Method>
	<Properties></Properties>
</DataType>