DRYing and documenting HDF5 loading code.
HDF5DataLayer source is now a list of filenames
HDF5 data now loaded into Blobs; cleaner interface
Making HDF5 blob data non-mutable for copy (minor)
Lint errors fixed, except still using stream.
minor
Merge pull request #203 from sergeyk/hdf5_data

HDF5DataLayer source now takes list of filenames, loads one at a time.