Vivaldi UI at low width window size

[S_Paternotte]

The Vivaldi UI should be robust towards low width window sizes.
See: https://forum.vivaldi.net/topic/37862/vivaldi-ui-at-low-resolutions

Find solutions for:

• extension icons getting stacked on each other
• zero width search field
• ...

[Gaëlle]

@S_Paternotte great request, thanks for asking for it.