Add basic date & time formatters using navigator language (#404)

Adjacent to #400 — while this isn't yet a proper localization pass, at
least dates & times will now use the user's browser language/locale
settings. When used in Browsertrix, this should ensure dates are
formatted more consistently, at least when the user has a locale with a
language matching one of the supported languages in Browsertrix set in
their browser settings.

Also adds tabular numerals in a few places (e.g. lists of dates/times).

src/item-info.ts

@@ -7,6 +7,7 @@ import prettyBytes from "pretty-bytes";
 import type { ItemType } from "./types";
 
 import "./components/labeled-field";
+import { dateTimeFormatter } from "./utils/dateTimeFormatter";
 
 // ===========================================================================
 class ItemInfo extends LitElement {
@@ -111,7 +112,9 @@ class ItemInfo extends LitElement {
           </wr-labeled-field>`
         : nothing}
       <wr-labeled-field label="Date Loaded" class="column is-2">
-        ${item!.ctime ? new Date(item!.ctime).toLocaleString() : nothing}
+        ${item!.ctime
+          ? dateTimeFormatter.format(new Date(item!.ctime))
+          : nothing}
       </wr-labeled-field>
       <wr-labeled-field label="Total Size" class="column is-2">
         ${prettyBytes(Number(item!.totalSize || item!.size || 0))}