Privacy: Allow disabling history, tab, and bookmark suggestions

There is not currently a way to disable history or open-tab suggestions in the vomnibar.

This is a privacy concern when using vimium away from home, as it may show sensitive information about items in history or tabs tabs in windows that are minimized or in another workspace. It should be possible to use vimium and the vomnibar without needing to keep your entire browser sterile enough to satisfy the most restrictive environments (school, work).

Simulating a keyword search provider (like the Firefox address bar's ^ * + % etc) would be excellent. This would allow a user to disable automatic suggestions then decide each time if they want to display their browsing history and open tabs to those near them.
Another reasonable config option for open tabs would be to only search tabs from the current window, allowing users to easily separate e.g. personal and work browser windows.

See also: #3078

No file or test is named. Start by tracing the vomnibar's history and open-tab suggestion behavior, then review the related discussion in #3078. Done should mean users can disable these suggestion sources and, if the chosen scope includes them, limit open-tab searches to the current window or invoke them explicitly.