backport of NO_RST switch from tlf-1.2.0 branch

- will be needed for contests which do not record any exchange (e.g.
  ARRLFD or CW Open)

- add new configuration switch NO_RST

- do not add RST into log and do not show RST if NO_RST is set,
  just add '---' instead

- suppress redisplay of RST after PgUp/PgDwn if NO_RST is set, as it
  does not make sense to change RST if no RST is used.

- document NO_RST in man page and add it to arrlfd rule file