Add a number widget to GT Magritte

[hellerve]

Currently we have no widget for numbers in GT Magritte (so the element builder just ignores them).

We should add a widget.

Cheers

[hellerve]

For now it re-uses the string widget; we should probably revisit this in the future.

[girba]

Is this still open?

[hellerve]

We have a working number description, but not a number widget. I think this would be a worthy addition, but maybe not part of this issue?

[girba]

I close it now. We can open another issue if we have the need for an extended widget.