[orangecontrib] normalization work

See merge request workflow/xas!17

- orange signal 'spectra' is renamed xas_obj
- update to the new orange way to define Input and Output
- add a converter widget to convert from xas object to data table

'Spectroscopy add on' compatibility

See merge request workflow/xas!16

Unit test pymca larch

See merge request workflow/xas!15

xftf fails because chi is not setted by exafs. Could it be computed from outside ?

Larch usability

See merge request workflow/xas!14

Add larch process orange contrib

Closes #6

See merge request workflow/xas!13