Rebrand to INBUXA: product name, protocol greetings, sign-in page, calendar templates, logos, README

One branding module (types::brand!) supplies the name to every protocol
greeting, the HTTP realm, the startup banner, Received headers, the
user agent, the IMAP ID response and calendar PRODIDs. The sign-in and
calendar pages take ihasmail's palette and font and the INBUXA logo, and
calendar emails embed the INBUXA lockup. Default calendar and address book
names follow. Protocol identifiers (urn:stalwart:jmap, vnd.stalwart Sieve
extensions) and upstream copyright notices are unchanged.

tests/resources/itip/vtimezone.txt

@@ -26,7 +26,7 @@ summary.dtstart: Time(ItipTime { start: 1794322800, tz_id: 433 })
 summary.summary: Text("Berlin meeting")
 BEGIN:VCALENDAR
 METHOD:REQUEST
-PRODID:-//Stalwart Labs LLC//Stalwart Server//EN
+PRODID:-//INBUXA//INBUXA Server//EN
 VERSION:2.0
 BEGIN:VEVENT
 SUMMARY:Berlin meeting
@@ -92,7 +92,7 @@ summary.dtstart: Time(ItipTime { start: 1794322800, tz_id: 433 })
 summary.summary: Text("Berlin meeting")
 BEGIN:VCALENDAR
 METHOD:REPLY
-PRODID:-//Stalwart Labs LLC//Stalwart Server//EN
+PRODID:-//INBUXA//INBUXA Server//EN
 VERSION:2.0
 BEGIN:VEVENT
 SUMMARY:Berlin meeting
@@ -144,7 +144,7 @@ summary.dtstart: Time(ItipTime { start: 1794322800, tz_id: 433 })
 summary.summary: Text("Berlin meeting")
 BEGIN:VCALENDAR
 METHOD:CANCEL
-PRODID:-//Stalwart Labs LLC//Stalwart Server//EN
+PRODID:-//INBUXA//INBUXA Server//EN
 VERSION:2.0
 BEGIN:VEVENT
 STATUS:CANCELLED
@@ -228,7 +228,7 @@ summary.dtstart: Time(ItipTime { start: 1794322800, tz_id: 433 })
 summary.summary: Text("Berlin meeting")
 BEGIN:VCALENDAR
 METHOD:REQUEST
-PRODID:-//Stalwart Labs LLC//Stalwart Server//EN
+PRODID:-//INBUXA//INBUXA Server//EN
 VERSION:2.0
 BEGIN:VEVENT
 SUMMARY:Berlin meeting