Add random string at the end of the default resource

When connecting for the first time or when creating a new account don't
use only 'profanity' as default resource.

Some server don't support having 2 connection with same resource. Using
profanity as default lead to deconnections.

src/xmpp/jid.h

@@ -57,5 +57,6 @@ char* create_fulljid(const char *const barejid, const char *const resource);
 char* get_nick_from_full_jid(const char *const full_room_jid);
 
 char* jid_fulljid_or_barejid(Jid *jid);
+char* jid_random_resource(void);
 
 #endif