[ComboTabBar] Use initStyleOption workaround only for Bespin theme

It is needed only with Bespin.
With other themes, it actually makes it worse.
[HistoryTreeView] Rewrite HistoryView to use same logic as BookmarksTreeView

It also fixes issue that middle click on item opened the url in both
current and new tab
[SideBars] Don't override cursor on scrollbars in History/Bookmarks sidebars