account: allow a "deposit all" option

In the past for lnd we had an issue where a user would try to send coins, but then needed to pay for fees, so they'd have to subtract an amount then try again, over and over again. We eventually add the `--sweepall` option in `SendCoins` to address this. We should add a similar flag for `pool accounts deposit` that lets the user deposit _all_ their coins (from the lnd wallet) into `poold`.

Start with the `pool accounts deposit` command and compare its behavior with lnd's `SendCoins --sweepall` option. Trace how the deposit amount is selected and verify that the completed behavior deposits all coins from the lnd wallet into poold while still handling fees.

Written by the indexing model from the issue text.