Add Mailing lists to Administration

A mailing list is an address that passes mail on to everyone on it. To
Stalwart it is its own object, x:MailingList, behind sysMailingList*, so
it gets its own section under Directory after Groups: search, fifty to a
page with each list's recipient count, and a panel to create, edit and
delete one.

Recipients are a property of the list, so unlike a group's members they
save with the rest of the panel. What Save sends for them is only what was
added and removed, one recipients/<address> pointer each -- the patch the
live server accepted -- so a recipient added elsewhere while the panel was
open is not taken out. They can be pasted several at a time, from a
spreadsheet column, a comma-separated line or Name <address>; anything with
an @ that is not an address stays in the box with a note. Past a dozen, a
filter narrows them.

That is all a list is in Stalwart -- no owners, moderation or posting
rules -- so that is all the panel offers.

The mock answers x:MailingList with two lists, the recipient set's live
shape, and the refusals a wrong address, a clash with an account and a
missing permission get.

Twenty-five new strings and one plural, in all nine catalogues.

ROADMAP.md

@@ -8,7 +8,7 @@ the rest is here because the answer is "no", not "not yet".
 
 See [KNOWN-ISSUES.md](KNOWN-ISSUES.md) for what is built but worth knowing about.
 
-- **Administration beyond accounts, groups and domains.** The Administration menu opens on a dashboard and manages accounts, groups and domains today — see [FEATURES.md](FEATURES.md#administration). Mailing lists, roles, DNS and ACME providers and tenants are Stalwart registry objects behind the same permission model, and each is a section to add rather than a design to invent; so is switching a domain's DNS, DKIM or certificate management, which is shown but not yet changed from ihasmail. The dashboard reads a handful of numbers and stops there. Managing queues, reading logs and changing server settings are not planned: they are operating the server, which is Stalwart's own interface's job, not managing the people on it.
+- **Administration beyond accounts, groups, mailing lists and domains.** The Administration menu opens on a dashboard and manages accounts, groups, mailing lists and domains today — see [FEATURES.md](FEATURES.md#administration). Roles, DNS and ACME providers and tenants are Stalwart registry objects behind the same permission model, and each is a section to add rather than a design to invent; so is switching a domain's DNS, DKIM or certificate management, which is shown but not yet changed from ihasmail. The dashboard reads a handful of numbers and stops there. Managing queues, reading logs and changing server settings are not planned: they are operating the server, which is Stalwart's own interface's job, not managing the people on it.
 - **Sharing a mail folder.** Stalwart stores the share and never delivers it; see [KNOWN-ISSUES.md](KNOWN-ISSUES.md). Withdrawn until the server does something with it. Sharing files, calendars and address books is unaffected and works.
 - **A scheduling view of its own**, for asking "when is everyone free next week?" without an event in hand. The grid itself is built and lives in the event editor — a row per participant, steppable, and clickable to place the event — which is where the question gets asked while you are arranging something. What is not built is the same thing as a destination you can visit with nothing in progress. Came out of [#172](https://github.com/Coffey-Labs/ihasmail/issues/172), which asked for a separate view and is closed by the panel: the reasoning for putting it in the editor is that a separate surface can only ever tell you a time you then retype, whereas one beside the event can set it. It stays here rather than in the tracker because nobody has yet said they want to ask the question on its own.
 - **Per-message actions from the message list on a touchscreen.** Reply, Forward and compose-as-new are on the list row's context menu, which is a right-click — and holding a row on a phone starts selection instead, so none of them are reachable there. They are all available inside a thread, which is where the actions on a single message belong; what is missing is the shortcut from the list. Fixing it means deciding what a long press should do when it already means something, which is a bigger question than the actions themselves.