Make the staff toolbar sticky by default or as an option

[Stuart Wright]

Simple tweak, really. The Staff toolbar really does need to be sticky by default.

/admin.php?styles/style-default.2/style-properties/group&group=headerNav
should have or use the same sticky options as for the main header.

I use

    <xf:comment>Moderators get a sticky moderator bar</xf:comment>
    <xf:if is="$xf.visitor.is_moderator">  
        <xf:css>
        .p-navSticky {top: 34px !important;}
        .p-staffBar {position: sticky;top: 0;z-index:400;}
        </xf:css>
    </xf:if>

in page_container, but it shouldn't be necessary.
Cheers.