fix(xmpp): obfuscate client identity in protocol exchanges

Modify version responses to return a generic client name and omit
version strings. Drop the "profanity." prefix from dynamically
generated JID resources. Spoof the XEP-0115 capabilities node URI to
prevent service discovery/presence fingerprinting. These adjustments
reduce the client's attack surface by minimizing identifiable metadata.

src/common.c

@@ -921,7 +921,7 @@ prof_date_time_format_iso8601(GDateTime* dt)
     return ret;
 }
 
-/* build profanity version string.
+/* build CProof version string.
  * example: 0.13.1dev.master.69d8c1f9
  */
 gchar*