Implement spec events

[gjermundgaraba]

As soon as the IBC Eureka events are finalized (cosmos/ibc#1165) we need to do a full cleanup of the events we currently emit from our contracts.

We likely have some unnecessary events, so the initial plan here is to remove the current events and only implement the spec events. After that, we can decide if we need more events (and if those should also go into the spec).

[sangier]

hey @serdar @gjermund , note that if at this stage we won't consider support for async acks and the multipayload, then the events are already pretty much aligned with the spec and with serdar suggestion. The minimum required parameters are emitted.
What we could remove are the event emitted in the ics20Transfer, but this would result in a very little gain on gas cost. I would prefer to keep the event emission there.

I would suggest to icebox this till we decide to implement multipayload and/or async acks.

[srdtrk]

1. Would multipayload only differ on ack events?
2. Maybe you can open a PR to remove unnecessary events? (I think we use some of those events in the tests but maybe you can come up with another way to test the same logic)

[sangier]

1. We would need to change sendPacket events too as in spec we emit a send_payload specific event in the multipayload case.
2. Gonna check this out.

[gjermundgaraba]

Did a quick check on removing emit ICS20Transfer(packetData, erc20Address); and it looks like it saves about 5k of gas to do so. I would say that we should remove anything that is not needed as we are trying to squeeze out as much performance as we can, and if this is not strictly needed, we should just get rid of it.

[sangier]

Ok, agreed. Will remove the transfer events so!

[srdtrk]

Let's also remove any other unnecessary events