GetFile acceptance test

The changeset in https://sbforge.org/jira/browse/BITMAG-169 gives a good idea of involved code.

Only the https://sbforge.org/display/BITMAG/Get+data+with+id1+from+fastest+pillar user story is covered by this GetFile prototype implementation and this acceptance test.

The remaining parts of the functionality described on https://sbforge.org/display/BITMAG/Get+File will be implemented and tested in later iterations