Expose layers and remove now-redundant params in Python interface

For now, only layer names and blobs are accessible, but more
functionality (layer Forward and Backward) could be added later.
Expose caffe.Net.params as an OrderedDict
Add names to the blobs returned by CaffeLayer

Even though these are redundant, this keeps the meaning of
CaffeBlob.name consistent for now, and will allow CaffeBlob construction
to be simplified.
Remove spurious constructors from CaffeBlob and CaffeBlobWrap

This prevents accidental construction of partially-specified blobs,
which could break the Python layer.
Add extra comment on vector_indexing_suite to _caffe.cpp