Metadata output from spectrumdata task

See merge request !106

E0 might be very wrong during online data processing

See merge request !105

the average raw noise was wrong in the noise widget

See merge request !104

Resolve "Plot chi(k)*k^n instead of chi(k)"

Closes #70

See merge request !103

Fix feedbacks from bm23

Closes #68 and #71

See merge request !101

Resolve "Plot “flat” group instead of “norm” if “make flat” is ticked"

Closes #72

See merge request !102

# Conflicts:
#	src/est/gui/XasObjectViewer.py

# This is the 1st commit message:

rework noise
   * make e_min and e_max relative to the edge
   * plot e_min and e_max
   * always make noise computed on the full spectrum. e_min and e_mask are used to compute the mean only
   * remove Spectrum.noise_savgol_energy
   * move '_SavitskyGolayNoiseOpts' to public

# The commit message #2 will be skipped:

# fix fb52fa55

   * make e_min and e_max relative to the edge
   * plot e_min and e_max
   * always make noise computed on the full spectrum. e_min and e_mask are used to compute the mean only
   * remove Spectrum.noise_savgol_energy
   * move '_SavitskyGolayNoiseOpts' to public

fully remove and clean process registration and h5 file link mecanism

See merge request !100

* process registration was used to keep trace of each processes and dump results. This will be done at another level in the future (probably by ewosk)
   * remove `Process.register_process` function (and call to it)
   * remove `_NexusDatasetDef` class which was used to define which field must be saved for a process
* remove saving_point widget: was using the regitered processes and needed for large number of spectrum. This is not the use case today and if we want to have such a mecanism it will be done another way in the future.
* remove `write_process` parameter from `XASWriter.dump_xas`
* XASObject:
   * remove `keep_process_flow` from constructor
   * remove `link_to_h5`, `has_linked_file`, `get_next_processing_index`, `register_processing`, `get_process_flow`, `clean_process_flow` and `copy_process_flow_to` functions
   * `to_dict`: remove `with_process_details` parameter and link mecanism
* update unit test