Add Groups to Administration

A group is a shared address and mailbox and the people who share it. To
Stalwart it is an x:Account of type Group, behind the same sysAccount*
permissions as a person, so it sits under Directory beside Accounts:
search, a page of fifty with each group's member count, and a panel to
create, edit and delete one.

Membership lives on the member, not the group. Members are the users whose
memberGroupIds name it, and adding or removing one is a single
memberGroupIds/<group> pointer on that user's account -- true or null --
which leaves their other groups alone. Changes apply straight away rather
than riding on Save, so the list is always what the server has. Nobody can
add or remove themselves, the same line the account panel draws at one's
own role.

A group's role is Default or Custom, not a person's User or Admin, and it
is what the group may do: in 0.16 a user's permissions come from their own
roles only, and a group gives its members what is shared with it. Only
roles the viewer could grant are offered.

Delete takes the members out first and then deletes the group, the order
a domain's keys go before the domain, because the registry keeps anything
another object names. A role that cannot change the members' accounts is
not offered a delete it could only half finish.

The mock's groups had a person's roles, accepted a memberGroupIds filter
without applying it, and answered a linked delete with the wrong shape;
all three follow the source now, and it refuses nested groups and
memberships of things that are not groups.

Nothing about groups has been run against a live server yet: production
has none, and every operation is a write. KNOWN-ISSUES says what was read
from source.

Thirty-five new strings, two of them plurals, 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 and domains.** The Administration menu opens on a dashboard and manages accounts and domains today — see [FEATURES.md](FEATURES.md#administration). Groups, 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 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.
 - **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.