Use config for class name of transactions relationship

Update HasAccountingJournalTransactions.php

Use config to determine class for accounting transactions relationship.

Use the config class name for journal transactions

Fix the journal::credit() and journal::debit() methods to use the transactions class name defined in the config.

Fix column name typo

1.0.1

Fix column typo: currency => currency_code

Various updates

• Laravel 9
• PHP 8.1
• More object interfaces
• More consistent table column names