ReaderCommand: correct plane count if 1 plane

If there were no planar axes, the plane count would end up 0 instead of
1. Fixed.
Convert: fix warning spacing

The warning for overwriting an existing image was missing a space.
SCIFIOConfig: add copying capabilities

Added a copying constructor to SCIFIOConfig, and implemented clone() to
take advantage of this new constructor. This should allow simple copying
of configurations, e.g. when specific settings need to be forced
temporarily.