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/src/jmap/principal/get.rs

@@ -54,7 +54,7 @@ pub async fn test(test: &TestServer) {
         "urn:ietf:params:jmap:submission": {},
         "urn:ietf:params:jmap:vacationresponse": {},
         "urn:ietf:params:jmap:sieve": {
-          "implementation": "Stalwart v1.0.0"
+          "implementation": "INBUXA v1.0.0"
         },
         "urn:ietf:params:jmap:blob": {},
         "urn:ietf:params:jmap:quota": {},