Make each run of Pathway Tools independent.

[ArnaudBelcour]

Right now, mpwt runs PathoLogic, checks errors, creates flat files (if the option has been used) and then moves the output. Each of these steps are made separately by sending all the input to one of the function with a starmap call.

But it could be useful to launch all of these steps independently for each organism. In this way, if there is an error, only the organism with the error will stop, the other will continue.

Also this could allow to delete the previous PGDB created in ptools-local (if the builds have passed) to decrease the amount of disk usage when dealing with a high number of organisms.

[ArnaudBelcour]

Instead of adding this as an option make it the default behavior of mpwt.

[ArnaudBelcour]

Added in the 0.7.0 (#72).