Display ilp errors

[michielbdejong]

It's important for the admin of an ilp-kit to know which of its peers cause failures.

One way to allow this is to look at the forwardedBy field of incoming ilp errors, and display the second one in the UI (the first one will always be the local connector).

See https://github.com/interledger/rfcs/blob/master/0003-interledger-protocol/0003-interledger-protocol.md#ilp-error-format

Also, the connector should check who appends to forwardedBy - for instance, I trust my own connector to state that an error message came in from a peer, but it should be impossible for a peer to spoof someone else's address as the last forwardedBy address.