[wallet] connect wallet with backend

[florianlenz]

Feature

We need to connect the pangea lib's wallet with the UI in order to send / receive eth.

Acceptance criteria

• [x] send eth
• [ ] receive eth
• [x] sync accounts

Additional information

• Keep the promise rejection in mind

[seland]

@florianlenz Do we need to do something to receive money?

[florianlenz]

Not really. We just need to display the correct address.