Allow user to specify to move/copy/link images

[bcipolli]

When converting, a user may want to move, copy, or symbolically link images from the original OpenFMri dataset.

Currently:

• By default, dummy functional files are created, and anatomical images are copied.
• The user can choose to copy the functional files as well through the function, but not via the command-line..

With this change:

• By default, dummy files are created for functional and anatomical images.
• Users can choose to move/copy/symbolically link the images (one parameter for both types of image)
• This choice is exposed on the command-line.

Testing:

• I tested that this works in Python. I haven't tested this on the command-line.

[chrisgorgo]

Thanks!