[WebView] Another approach to window.onbeforeunload handling

Don't try to load empty url just to check for beforeunload event.
Explicitly evaluate the window.onbeforeunload function instead.
[ListItems] Apply workaround only for Fusion style

It actually breaks other styles ...
Fixes 2105b48ca45cca9c079ca5e7b5433662e97d6a41
[ComboTabBar] Hopefully fixed all issues with wrong mouseover state for tabs

Repaint the whole tabbar on enter and leave events, so all tabs are
rendered with correct mouseover state.
[Shortcuts] Ctrl+W shortcut no longer closes a pinned tab

Pinned tab can now only be closed from tab context menu
[BookmarksToolbar] Fixed window flicker when showing toolbar
[TabPreview] Disable tab previews by default

They are too intrusive, so don't force them by default
[BookmarksToolbar] Don't hardcode height of buttons

Also don't "hide" (=resize only to layout spacing * 2) toolbar
when there is no bookmark in it.
[TabTooltips] Fixed tooltips disappearing on (un)pinning tabs
[NewTabFlags] Fixed incorrect usage of Qz::NewTabPositionFlags
[Flicker] Fixed flicker when opening new tabs with sites that loads instantly

Eg. this happens for internal qupzilla: pages
Also early set locationbar's url to newly opened tab's url.