Data Viewer should display columns that include only only null values

[vdestraitt]

If a column has only null values, it is just excluded and is not displayed in the dataviewer. It is not the expected behaviour and we should display the column even if full of null values.

[vdestraitt]

In other contexts, the problem does not occur. So the problem seems to appear between the server response and the display. We need a fix in our app.js probably.