BUG: Provide initial input_type value in itkTemplate
BUG: Provide initial input_type value in itkTemplate

To prevent errors like:

    File "/home/matt/bin/ITK-Wrap-MinSizeRel/Wrapping/Generators/Python/itkTemplate.py",
    line 515, in New
        if not input_type:
        UnboundLocalError: local variable 'input_type' referenced before assignment

Also, improve corresponding error message to include the `ttype` keyword
parameter option.

malaterre/ITK,BRAINSia/ITK,Kitware/ITK,vfonov/ITK,InsightSoftwareConsortium/ITK,thewtex/ITK,Kitware/ITK,vfonov/ITK,thewtex/ITK,malaterre/ITK,malaterre/ITK,BRAINSia/ITK,thewtex/ITK,malaterre/ITK,richardbeare/ITK,richardbeare/ITK,LucasGandel/ITK,BRAINSia/ITK,thewtex/ITK,thewtex/ITK,hjmjohnson/ITK,thewtex/ITK,hjmjohnson/ITK,LucasGandel/ITK,hjmjohnson/ITK,LucasGandel/ITK,Kitware/ITK,LucasGandel/ITK,vfonov/ITK,InsightSoftwareConsortium/ITK,LucasGandel/ITK,InsightSoftwareConsortium/ITK,vfonov/ITK,BRAINSia/ITK,LucasGandel/ITK,LucasGandel/ITK,malaterre/ITK,Kitware/ITK,LucasGandel/ITK,malaterre/ITK,vfonov/ITK,vfonov/ITK,vfonov/ITK,InsightSoftwareConsortium/ITK,BRAINSia/ITK,BRAINSia/ITK,richardbeare/ITK,malaterre/ITK,BRAINSia/ITK,InsightSoftwareConsortium/ITK,malaterre/ITK,richardbeare/ITK,malaterre/ITK,Kitware/ITK,richardbeare/ITK,hjmjohnson/ITK,hjmjohnson/ITK,InsightSoftwareConsortium/ITK,vfonov/ITK,Kitware/ITK,Kitware/ITK,hjmjohnson/ITK,richardbeare/ITK,thewtex/ITK,hjmjohnson/ITK,vfonov/ITK,richardbeare/ITK,InsightSoftwareConsortium/ITK