Syntax to set width of number fields

[Masacroso]

In practice generally we don't want a number field larger than 2-3 digits, so I think it would be interesting to add the possibility to setup the width of the number fields to avoid using CSS. By example you can setup the width of all number fields in the whole notebook with pluto-output input[type=number] { width: ... ; }, or for some specific cell using it id instead of the pluto-output tag.

[fonsp]

This should be an inline style of the <input> element