Properly manage transaction nonces

[raucao]

See dcbce66 for hotfix that doesn't really fix the underlying issue with ethers.js' wallet nonce management.

[bumi]

can we do a eth_gettransactioncount on boot or regularly, store that number and then manually increment the nonce everytime we've sent a transaction?

something like (pseudo code):

let nonce = await provider.getTransactionCount('pending');
nonce++;
[contirbution1, contribution2].forEach(c => {
  await kredits.Contribution.add(attrs, {nonce});
  nonce++;
})

[bumi]

we could maybe use ether.js's waitForTransaction to wait until the transaction is mined and then increment the nonce (or do a provider.getTransactionCount('pending') again) and then do the next transaction.