Prevent using get_me with input

[orsinium]

1. Make get_me return a new Me type instead of Peer.
2. This type can be used only with get_settings or for equality comparison with Peer.

While you can, if you really want, convert Me to Peer by iterating over Peers and picking the one that equals to Me (or going through into_u8 -> from_u8), it would require deliberately going out of your way to shoot yourself in the foot. So, the change should prevent the most common pitfalls, like read_pad(get_me()).

See firefly-zero/firefly-runtime#9.

[applejag]

LGTM