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/common/src/manager/boot.rs

@@ -38,7 +38,8 @@ pub struct IpcReceivers {
 }
 
 const HELP: &str = concat!(
-    "Stalwart Server v",
+    types::brand_server!(),
+    " v",
     env!("CARGO_PKG_VERSION"),
     r#"