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/rfc6638_recurring.txt

@@ -47,7 +47,7 @@ summary.rrule: Rrule(ICalendarRecurrenceRule { freq: Daily, until: None, count:
 summary.summary: Text("Review Internet-Draft")
 BEGIN:VCALENDAR
 METHOD:REQUEST
-PRODID:-//Stalwart Labs LLC//Stalwart Server//EN
+PRODID:-//INBUXA//INBUXA Server//EN
 VERSION:2.0
 BEGIN:VEVENT
 SUMMARY:Review Internet-Draft
@@ -89,7 +89,7 @@ END:VCALENDAR
 # Make sure the participant receives the event
 > get [email protected] 9263504FD3AD
 BEGIN:VCALENDAR
-PRODID:-//Stalwart Labs LLC//Stalwart Server//EN
+PRODID:-//INBUXA//INBUXA Server//EN
 VERSION:2.0
 BEGIN:VEVENT
 SUMMARY:Review Internet-Draft
@@ -185,7 +185,7 @@ summary.rrule: Rrule(ICalendarRecurrenceRule { freq: Daily, until: None, count:
 summary.summary: Text("Review Internet-Draft")
 BEGIN:VCALENDAR
 METHOD:REPLY
-PRODID:-//Stalwart Labs LLC//Stalwart Server//EN
+PRODID:-//INBUXA//INBUXA Server//EN
 VERSION:2.0
 BEGIN:VEVENT
 SUMMARY:Review Internet-Draft
@@ -343,7 +343,7 @@ summary.rrule: Rrule(ICalendarRecurrenceRule { freq: Daily, until: None, count:
 summary.summary: Text("Review Internet-Draft")
 BEGIN:VCALENDAR
 METHOD:REPLY
-PRODID:-//Stalwart Labs LLC//Stalwart Server//EN
+PRODID:-//INBUXA//INBUXA Server//EN
 VERSION:2.0
 BEGIN:VEVENT
 SUMMARY:Review Internet-Draft