Resolve "Bslz4 is not allowed for tomography data ..."

Closes #3075 (closed)

In this MR the data compression is optional (set with SCAN_SAVING.data_compression). By default it is gzip so that the HDF5 file can the read in any environment which has hdf5. The bitshuffle compression is better but requires installing custom HDF5 filters to read (easy in python but not in other languages like matlab).