[h5] DataArray: fix removal of polynomCoefficients

polynom_coefficients is not an attribute but a dataset in
hdf5, so removing it must remove the dataset not an
attribute. Add a missing test for it.
DataArray::getData: add support expansionOrigin
[test] checks for expansionOrigin (+ polynomial)
Merge pull request #379 from gicmo/expansionOrigin

DataArray::getData: Add support for expansionOrigin
Using "index" instead of "size_t" in "Dump.cpp" to avoid warning
Again fixing warnings due to "index" vs "size_t"
util::applyPolynomial: accept array data
Merge pull request #381 from balint42/nixtool

Using "index" instead of "size_t" in "Dump.cpp" to avoid warning
util::applyPolynomial: apply origin without coeff.
Merge pull request #382 from gicmo/getdata_poly

Move work from DataArray:getData to util::applyPolynomial, 
looks good to me -> merge ;-)
nix-bench: add foundations for benchmark tool
Merge pull request #383 from gicmo/benchmarking

nix-bench: add foundations for benchmark tool