Update required/recommended protocol versions.

  Cons=1 is the old format of consensuses, without ed25519 keys. It
  is no longer required or recommended.

  Cons=2 is the new format of consensuses, with ed25519 keys. It
  is now required.

  (Similarly for Desc=1,2 and Microdesc=1,2)

No supported client or relay versions should be affected by this
change, since these versions are supported by clients and relays
running 0.2.9 and later.  It will only take effect once enough
authorities vote for it.

Closes ticket 40162.