refactor: update account service to support sub accounts

[jackson-dean]

Changes the way accounts are stored to support sub accounts.
An overview of the storage strategy:

• We continue to store "root" accounts (accounts derived with account number 0)
  in a users key in local storage that is keyed on the public key of the root account.
• All subaccounts are stored in a subAccounts property on the root account. These subaccounts
  consist of the following props: { accountNumber, lastLoginTimestamp, isHidden }. The public key
  can be derived from this information combined with the seed stored on the root user.
• We have a reverse lookup map that maps subaccount public keys back to their root account public key.
  We need this to support look up by public key when a consuming application passes us a public key for
  the logged in user.

NOTE: There is nothing special about the root account. It is only for historical reasons that we key
the common data (seed, mnemonic, etc) under this account's public key. In practice, all accounts are
derived the same and all sub accounts are fully fledged and unique "owner" accounts that can be
issued their own derived keys and can sign with their own public/private keys.

[jackson-dean]

Current dependencies on/for this PR:

• main
  • PR chore: code formatting only #262
    • PR chore: update configs only #263
      • PR refactor: update account service to support sub accounts #264 👈
        • PR fix avatar directive default photo #274
        • PR feature: new component for sub account UI #266
          • PR chore: update copy per Ed's request #272
          • PR feature: add feature flag guard for new account select component #268
            • PR feature: backup seed component #269
              • PR feature: add balance to account selector UI #270
                • PR migrate swal to mat dialog #273
                  • PR update button styles #277
                  • PR review feedback and bug fixes #279
                • PR fix: consider users that have already been issued a derived key #271
          • PR chore: update copy per Ed's request #267
        • PR fix: fix broken avatar directive #265

This comment was auto-generated by Graphite.