Added find_duplicates method to Expense
Fixing duplication check tests for Expense
Testing duplication check methods

Added example of what seems to work to find duplicates as they are
introduced instead of looking through all records everytime
Added 2 columns for duplication check to Expense
Updated TODO.txt
Updated TODO, removed duplication task
Added duplication check tests

All duplication tests pass
Added ExpenseNotes for duplication notes in Expenses