HDF5: import less "nix" namespaces in cpp files

That is nix and nix::hdf5.
HDF5: Don't import all of boost namespace

Especially only for 4 usages.
[test] don't import nix::hdf5 namespace
DataIO → DataSet [renamed]
[travis] add -p to preserve paths for gcov

Because we have two files called DataSet.hpp now
Rename DataSet.[c|h]pp to DataSetHDF5.[c|h]pp

The HDF5 DataSet, not the toplevel one.
Merge pull request #409 from gicmo/dataio_rename

DataIO → DataSet