Emit warnings for fallible Bridge pool relays

[sug0]

Partially solves #1292
(Missing validator set update UX improvements)

[cwgoes]

I'm a little bit confused. What does it mean for an event to have been relayed, but not have a quorum of validator signatures? I thought the Ethereum-side contracts checked that all transfers from Namada have a quorum of validator signatures - shouldn't it be impossible to relay an event until it does?

[sug0]

@cwgoes here's the scenario:

1. you relay some transfers in the bridge pool with nonce $N$
2. the contract gets updated with nonce $N+1$
3. the event arrives in namada, and gets a quorum of votes behind it
4. namada's bridge pool nonce is incremented to $N+1$
5. a bridge pool merkle root is signed together with $N+1$
6. a quorum of nodes agree on the new merkle root signed together with $N+1$
7. finally, a new relay may be done for $N+1$

there's a bit of delay between relays because of this flow

[cwgoes]

Ah, you mean a quorum of validators agreeing on step (3), that the Ethereum-side contracts have confirmed the transfers. That makes sense but I think we're overloading the word "relay" a bit much, maybe we could say "relayed to Ethereum" or "relayed from Ethereum" so that it's not ambiguous?