* Replace Google with DuckDuckGo for optional fallback favicon fetch URL
Modify the work initially done in #36, and most recently modified in #1786,
to use DuckDuckGo's https://icons.duckduckgo.com/ip3/www.example.com.ico
favicon endpoint.
Fixes#2258
* Close failed favicon fetch progress bars
Name the UrlFetchProgressDialog() with the corresponding URL in order to
be identified by name by its parent when the failed request is handeled
in EditWidgetIcons::fetchFinished(). fetchFinished() retrieves the
relevant UrlFetchProgressDialog() and calls close() on it.
Fixes: #2265
* Add Standalone Password Generator. Closes#18
* Add an entropy meter for passwords. Closes#84
* Don't require password repeat when it is visible. Fixes#27