Don't add payee to transaction if it's not defined

[nielsmaerten]

Describe the bug
Payee parsing (currently in beta) sometimes results in a payee_name field like this:

• " ": just a bunch of spaces, no actually useful data

This causes YNAB's payee matching to trip up, causing duplicate and/or incorrect payees

Expected behavior
If there's no useful data in the payee field, it should be omitted from the payload to YNAB

Screenshots

Desktop (please complete the following information):

• OS: Windows
• Version: 1.1.1
• Did you install ynab-buddy using NPM? yes

Additional context
Add any other context about the problem here.