Fixed bug in processors: used Block class for reading alignment file. Until recent changes (introduction of Alignment/Block._append_columns) it worked out fine. But practically, we used alignment API: we created an empty object and called append_file on it. For blocks this resulted in a block that did not know it's alignment. Recent changes in implementation caused blocks to actually have their own specific methods besides constructor, and these methods use knowlege of alignment a block belongs to. Hence, the previous behaviour was a bug.