Add per-site configuration for matched entry sort order

[luckyrat]

New setting: “Sort matched entries by:” "Best match", "Title", "Username" (dropdown, including the usual "Inherit" option when rendered within a specific site config editor)

Explanatory note under the setting: “This has no impact on which entry is auto-filled or auto-submitted”

Something to watch out for is whether work on replacing the current options page with a VueJS approach would result in some wasted effort. If you're taking this issue on in December 2020 or later, please check first whether there is any ongoing work in that area that might conflict.

matchingLogin =
                    orderedEntriesWithPreference.find(e => e.isPreferredMatch) ||
                    orderedEntriesWithPreference[0];

needs replacing with something that always uses the best match as its fallback but other than that, most of the behavioural changes that the setting drives will be modifications to the formFilling.ts:sortMatchedEntries function. The result of that is distributed to both the old iframe in-page panel list of matched entries and the list within the main popup.