Add ability to obtain weak plan snapshots

[haz]

It would be useful to have the ability to export certain weak plan configurations (initial state / goal specification) for weak planning problems encountered during the search. This could be used to further analyze especially difficult or problematic weak planning problems posed to the FD sub-solver. The steps required:

1. Have a debug flag output a uniqe id for each weak planning invocation.
2. Have an input parameter available that exports a problem.pddl file based on the unique id.