change the config parser to use default_orientation instead of new_container_orientation

It’s a shorter and probably more meaningful description as it is not
immediately clear what a container exactly is when first installing i3.

src/cfgparse.l

@@ -92,7 +92,7 @@ set[^\n]*                       { return TOKCOMMENT; }
 ipc-socket                      { BEGIN(BIND_AWS_COND); return TOKIPCSOCKET; }
 ipc_socket                      { BEGIN(BIND_AWS_COND); return TOKIPCSOCKET; }
 restart_state                   { BEGIN(BIND_AWS_COND); return TOKRESTARTSTATE; }
-new_container_orientation       { return TOK_ORIENTATION; }
+default_orientation             { return TOK_ORIENTATION; }
 horizontal                      { return TOK_HORIZ; }
 vertical                        { return TOK_VERT; }
 auto                            { return TOK_AUTO; }