Add a check to delete unfinished PathoLogic build.

[ArnaudBelcour]

If mpwt is killed during a run, Pathway Tools could not have finished the build of some species (they do not contain all the reactions/pathways in their metabolic network).

After this, if mpwt is re-run it will not launch again Pathway Tools for these PGDBs. To avoid this issue, mpwt should check the pathologic.log file of already finished PGDB to see if the previous build has been successful.
If not, mpwt should delete these unfinished PGDB and re-run Pathway Tools on them.

[ArnaudBelcour]

Added in #50.