Improvements to image_datahandler:
 - add patchrandoffset
 - support for validity images
 - bug fixes

Properly modify the .proto file to handle new parameters instead of directly modifying deepnet_pb2.py.
Add cropped mass_roads dataset.  Include training data.  Use patchrandoffset on training data.  No longer use overlapping patches.
Merge branch 'aerial_images' of https://github.com/mbrubake/deepnet into aerial_images