Make search engines toggleable, and most opt-in

[KevinPayravi]

Indie Wiki Buddy started with support for filtering on Google, Bing, and DuckDuckGo. It's since grown to support 10 search engines. Most people, however, only use one or two for their day-to-day.

IWB should let uses toggle which search engines IWB runs on, and IWB should only have access to the search engines that the user enables.

We should also consider search engines being opt-in, for improved privacy. IWB's settings page opens on-install, which is where users could choose which search engines they'd like IWB to run on. Opt-in search engines also brings the additional benefit of making updates more seamless. Currently, when we add support for a new search engine, we add that search engine to the manifest.json. This requires the user to accept the new access when the extension updates, which is disruptive and causes concern about why IWB is requesting access to new sites. By having search engines be opt-in, these permission requests won't happen on-update.

For a good out-of-box experience, we could perhaps include access to the most popular search engines by default (Google, Bing, DuckDuckGo?), and then let users toggle off and on as they see fit.

If we do make search engines opt-in, there's an open question about how we want to manage existing users. Existing users would go from having their search engines being filtered to suddenly not. We'll want an elegant way to transition these users (e.g. open a tab explaining the update with opt-in settings).