* _NexusDatasetDef: can now have some units defined by latex: `units_latex`
* _NexusSpectrumDef: can now have a `title` and a `title_latex` defined

Signed-off-by: payno <henri.payno@gmail.com>

[orangecontrib][larch] add a call to `_updateProcess` on larch widget initialization to insure `_larchSettings` is updated if there is no modification of the parameters