Implemented <dataflow> and <compute> node, removed any use of <proto> in tests.
Renamed prototype tests to dataflow tests. Added new complex test case.
Changed internal behavior of order mapping.

If an keep filter is applied with order mapping, the channels in the
resulting map have now the SAME order of the names in the order mapping.

This is important, so that the order of output parameters declared with the "out"
attribut of <dataflow> is preservered.