Add flipcause.com to yellowlist

[ghostwords]

Examples:

• http://matplotlib.org (click either Support button on the right-hand side)
• https://veinternational.org/get-involved/donate/ (embedded donation form)
• http://fcclainc.org/ (Support button on page bottom)
• http://www.opvrs.com/get-involved.html (embedded form)

[ghostwords]

@andresbase Should we be reaching out to embedded widget providers like this asking if they would adopt our DNT policy?

[ghostwords]

I see a WEBSVR: newweb2 session cookie from https://www.flipcause.com/widget/... and a ci_session: LONG_ENCODED_STRING session cookie from https://www.flipcause.com/widget/give_now/....

We might want to ignore session cookies: #1545.

[andresbase]

It's a good idea reaching out to them, I'll send them an email.