Brand the webmail INBUXA: name, mark and wordmark

INBUXA is a product suite and ihasmail an independent product, so INBUXA's
webmail says INBUXA: the sign-in page, header, page title, installed-app name
and About page. The wordmark is drawn in the current text color. ihasmail's
version and AGPL source line stay as its credit. Two new strings, in all nine
catalogues; three Stalwart-only ones are no longer used.

INBUXA.md

@@ -20,11 +20,22 @@ keep up. Nothing here is pushed there.
   no address: only whether this is the person's own device, then the server's
   page takes it from there. With several servers, the address comes first,
   since its domain picks the server.
+- **Branded INBUXA.** INBUXA is a product suite, and its webmail carries the
+  INBUXA name, mark and wordmark, so it can't be taken for public ihasmail,
+  which stays an independent product. The default `APP_NAME` is `INBUXA`; the
+  sign-in page, header, page title, installed-app name and About page say
+  INBUXA. ihasmail's version and AGPL source line stay as its credit. Set
+  `APP_NAME` to something else and that name shows as text, as in public
+  ihasmail.
 - **Tenants are offered on every server**, whatever edition it reports.
   `SHOW_ENTERPRISE_NOTICES` still adds the notice for an upstream Stalwart.
 
 ## Configuration
 
+**Before any deployment, set `SOURCE_URL`** to where this fork's source is
+published. The AGPL's offer has to point at the source of the code that's
+running, and the default still points at public ihasmail.
+
 Server sign-in is on when `OAUTH_CLIENT_SECRET` is set. Without it,
 ihasmail-inbuxa keeps public ihasmail's password form.