Update a contact on re-import rather than skipping it

#228 skipped a vCard whose UID the book already held. The reporter asked for
the opposite on #174 and he is right: the reason to import a file a second
time is usually that the first one was not right, so skipping means a
corrected export corrects nothing.

A merge, not a replacement. Properties the file carries overwrite what is
here; properties it does not mention are left alone, so a phone number added
in ihasmail after the first import survives a re-import of the original file.
The cost is that a field genuinely deleted at the source stays here, which is
the better way to be wrong -- the other way round loses work nobody asked to
lose. Worth confirming with him rather than assuming.

`addressBookIds` is left off the patch. The card is already in this book, so
saying it again says nothing, and saying it on a card that is also in another
book would move it.

Creates and updates now share one batch budget. Stalwart counts every object
in a /set together, so batching the halves separately would send 300 new and
300 changed as two calls of 300 and be refused for a limit of 500 that neither
half exceeds.

LDIF is untouched and still reports look-alikes without acting on them, since
what it should match on is the question still open on #223. Both imports keep
one answer shape so a caller need not know which it called; LDIF's `updated`
is always 0, which is the honest number rather than a missing field.

The message a vCard attached to a message shows changes with it: the newer
copy now wins instead of being dropped, so it says the contact was brought up
to date rather than that nothing was added.

Refs #223.

web/src/locales/ja.ts

@@ -1061,10 +1061,11 @@ export const catalog: Catalog = {
     "Nothing unread here": "ここに未読はありません",
   },
   plurals: {
+    "Updated {n} contacts, nothing new": { other: "{n} 件の連絡先を更新しました。新規はありません" },
+    "{n} updated": { other: "{n} 件を更新" },
+    "Updated {n} contacts you already had": { other: "すでにある連絡先 {n} 件を更新しました" },
     "{n} of them look like contacts you already had": { other: "うち {n} 件はすでにある連絡先に似ています" },
     "Your administrator changed {n} settings": { other: "管理者が {n} 件の設定を変更しました" },
-    "Already here: {n} contacts, nothing imported": { other: "すでに存在: {n} 件、インポートなし" },
-    "All {n} are already in your contacts": { other: "{n} 件はすでに連絡先にあります" },
     "Exported {n} events": { other: "{n} 件の予定をエクスポートしました" },
     "Imported {n} events": { other: "{n} 件の予定をインポートしました" },
     "Already here: {n} events, nothing imported": { other: "すでに存在: {n} 件、インポートなし" },