Invoice intake agent - updater

1. Keep this folder anywhere, for example on the desktop.
2. Double-click update.bat (Windows) or update.command (Mac). A page opens in your browser.
   Mac: if it says the file cannot be opened, right-click it, choose Open, then Open again.
3. On the page, click "Install the latest version" the first time, or "Update" later,
   then "Start the app".

The app lives in the "app" folder next to these files. Your settings, the Gmail token and
the invoices are in app/data and are kept when you update or change version.

Needs Python 3 (from python.org - on Windows tick "Add python.exe to PATH" in the installer).
