fixing bug where extraction radius was assumed to be the number trailing the 'r' character in the file names; the true radius sits in the header of the data file

Added two routines to the CoRe_idx() that allows to update the index from a CoRe_md() metadata list and to write to a JSON file with specific keys from a template. Added a script to write the index JSON reading from all the metadta_data.txt of the DB

Bugfix for energy calculation, improved logic a bit (but still assumes the same modes at each extraction radius). Added more test data to have same number of modes for the two radii. Updated tutorials.

Debugged the create/read_dset h5 routines and added their use in one tutorial. These are the preferred method to create the CoRe data.h5.

Added more general (and simpler) methods to read/write files to group/dataset to h5. These do not enforce the CoRe convention but are more general, hence preferable. To be tested.