## Issue Addressed
Addresses #2557
## Proposed Changes
Adds the `lighthouse validator-manager` command, which provides:
- `lighthouse validator-manager create`
- Creates a `validators.json` file and a `deposits.json` (same format as https://github.com/ethereum/staking-deposit-cli)
- `lighthouse validator-manager import`
- Imports validators from a `validators.json` file to the VC via the HTTP API.
- `lighthouse validator-manager move`
- Moves validators from one VC to the other, utilizing only the VC API.
## Additional Info
In 98bcb947c I've reduced some VC `ERRO` and `CRIT` warnings to `WARN` or `DEBG` for the case where a pubkey is missing from the validator store. These were being triggered when we removed a validator but still had it in caches. It seems to me that `UnknownPubkey` will only happen in the case where we've removed a validator, so downgrading the logs is prudent. All the logs are `DEBG` apart from attestations and blocks which are `WARN`. I thought having *some* logging about this condition might help us down the track.
In 856cd7e37d I've made the VC delete the corresponding password file when it's deleting a keystore. This seemed like nice hygiene. Notably, it'll only delete that password file after it scans the validator definitions and finds that no other validator is also using that password file.
