remove padding layer
some cleanup - lowercase layer class member variable names
alphabetize classes in vision_layers.hpp
some naming standardization: ImagesLayer -> ImageDataLayer (like other
data layers), and load_hdf5_file_data -> LoadHDF5FileData
make test_protobuf use NONE for dummy layer instead of SPLIT
update deprecated protos to latest dev versions
incorporate WindowDataLayer into V0Upgrade and add tests