got rid of the need to create a whole new datacube to store the shifted data.  This should be more efficient in memory.
added in some recommendations in the coalignment method
coalignment method now returns a new mapcube
changed some comments in the clipping code
removed print statement that was used for debugging
used a try/except block to warn about missing coalignment
added import error trapping for the coalignment method
warning now appears when coalign method is attempted to be used when the required module is not present.
changing the catching of the lack of match_template: raise an ImportError error in function that requires it.
Merge pull request #904 from wafels/ji_image_alignment

got rid of the need to create a whole new datacube to store the shifted ...