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.

crates/managesieve/src/lib.rs

@@ -9,7 +9,7 @@
 pub mod core;
 pub mod op;
 
-static SERVER_GREETING: &str = "Stalwart ManageSieve at your service.";
+static SERVER_GREETING: &str = concat!(types::brand!(), " ManageSieve at your service.");
 
 #[cfg(test)]
 mod tests {