Add larch process in core

See merge request workflow/xas!11

[core][larch] fix creation of the new secptrum object when overwrite is True in larch process wrappers

fix 6f127e5e, process, progress.. should still be part of xas.process

[io] rework h5 output to use Nexus format

Closes #7 and #11

See merge request workflow/xas!10

Allows to reexecute all treatment from a .h5 containing the process definition.

[orangecontrib] rework the display for ft and kweight. kWeight is displaying nothing for the time beeing.

Everything is displayed by ft througt to 'spectrum' display: the window and the ftintensity

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