Extending ags_file.dtd and ags_file.xsd in view of release 0.4.0

Release 0.4.0 of Advanced Gtk+ Sequencer gets some extends in saving files. As possible it will be compatible with ags_file-0_3_12.dtd.

It is planned to move creation code of recalls into a line member factory. To support saving your changes within gui it is necessary to extend the file format. AgsLine will be some kind of XML based.

All GUI components inheriting from AgsMachine, AgsPad and AgsLine need to be updated.