removed unanlysable command, raise PhylogenyProgramError

* PhylogenyProgramError is raised instead of PhymlError and RaxmlError
(duh!)
* moved unanalysable variable to fabricate_result() in subset.py
updated subset.unanlysable commands to subset.fabricated
added fabricate() for unanalyzable subsets
moved the fabricate function to processor

* also changed "unanalysable" variable to "fabricated". Now mark
subsets as "fabricated" if they use the fabricate_result() function