Wrap img proc tools

Contains the function files required for image processing using vistrails. Current function groups focus on:
Thresholding
Morphological filtering
Volume transformation
Image filtering
Histogram analysis

Concurrent pull requests have been made to VTTools, and userpackages and the files in those PR's are required in order for these functions to be incorporated into our vistrails product.
put in and `else` which raises an exception.  Is it stands if you pass in an invalid value it will raise `NameError` that `output` is not defined.