Add a logfile parameter to import/export tools

Updated description:

Add a command line option to direct all output to a file instead of STDOUT/STDERR. This makes it easier for users to capture output in environments/situations where redirecting filehandles is non-trivial (e.g. Windows).

Original description:

For long running dump/restores it is useful to have the progress and/or errors print out to a logfile location. I understand you could simply redirect the output to a logfile location, however that makes it less convenient for long running operations (hours? days?). It would be much simpler to run these jobs as detached processes rather than tie them to shell instances.