In fact instead of having to repeat those definitions n times we should have some king of a database defining those once for all

- rename '_volurm_for' to 'map_to'. Remove dim1 and dim2 parameter: now useless because we can dircetly get them for the spectra class

# Conflicts:
#	est/core/process/process.py
#	est/core/process/pymca/test/test_io.py
#	est/core/process/test/test_roi.py
#	est/core/test/test_types.py
#	est/io/io.py
#	est/setup.py

# Conflicts:
#	est/core/types.py
#	requirements.txt

This require the creation of some helpers to link io and XasObject, this is the goal of xas.core.io.

- now process can take an output and an output_dict for storing the result in a multiprocessing.Proxy object
- rework process action to avoid several call to pymca `processSpectrum` function
- add an option to XasObject `to_dict` function to simply store raw data (which is the reference), but also to keep processing results to be used later.
This is need for the 'non gui' workflow processing which uses a dictionnary instead of a XasObject.

Conflicts:
	xas/core/types.py

- simplify the bases structure Spectrum and XASObject to be more generic and continue workfing with pymca.

- create callable classes in order to get the setParameters function.
- copy parameters to the xas_obj processed.
- /close #2

[unit test] add a workflow unit test with the four first process. Should ne executed without any log error from pymca