Value lists - add a new column to handle display values without underscore

[jpdupuy]

The content of the columns "value_fr" or "value_en" contains the underscore character replacing the space character.

This is not very nice to display these values in the dropdown lists in the QGIS forms.
I understood this was necessary for the Interlis export, but it would be nice to have an or several additional column in every value list table so that the translation (with the proper french character set and no underscore) can be handled.
The development guide should also be enriched to explain how to handle this case for future TEKSI modules.

[sjib]

Coordinate with qwat and tww developments

[rbovard]

Value lists - add a new column to handle display values without underscore + and with proper character

[sjib]

Do as common project over all TEKSI modules