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/pop3/src/lib.rs

@@ -22,7 +22,7 @@ pub mod op;
 pub mod protocol;
 pub mod session;
 
-static SERVER_GREETING: &str = "+OK Stalwart POP3 at your service.\r\n";
+static SERVER_GREETING: &str = concat!("+OK ", types::brand!(), " POP3 at your service.\r\n");
 
 #[derive(Clone)]
 pub struct Pop3SessionManager {