Add finanzfluss.de icon

[FeR0se]

Requirements

Go over all the following points, and put an x in all the boxes that apply.

• [ x ] My issuer icon is fully vector and does not contain (parts of) a JPG/PNG/etc.
• [ x ] My issuer icon contains the original brand logo, not that from an icon pack.
• [ x ] My issuer icon is somewhat square, so it's nicely visible in the app.
• [ x ] My issuer icon starts and ends with the <svg> element.
• [ x ] My issuer icon is scalable (it uses viewBox instead of a static width/height).
• [ x ] My issuer icon does not contain whitespace around the SVG (this JSFiddle could help to remove whitespace).
• [ x ] My issuer icon does not include the doctype element.
• [ x ] My issuer icon directory and file name is lowercase.
• [ x ] My issuer icon directory and file are in the vectors/[domain name]/ folder.
• [ x ] My pull request contains just one icon.