Counterparty for connections and channels must not have any Option<> type

[plafer]

Summary of Bug

The Counterparty structs should look like:

/// Connection
pub struct Counterparty {
    client_id: ClientId,
    pub connection_id: ConnectionId, // currently `Option<ConnectionId>`
    prefix: CommitmentPrefix,
}

/// Channel
pub struct Counterparty {
    pub port_id: PortId,
    pub channel_id: ChannelId, // currently `Option<ChannelId>`
}

In other words, a Counterparty must have a valid connection/channel id. The current version is incorrect.

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[plafer]

To be implemented when we remove the crossing hellos logic (#143).

[plafer]

This is not true. The {connection,channel}_id will be None after OpenInit.