Add a warning before showing recaptcha in zero-rating mode

[gimite]

It should warn that zero-rating is not applied.

[kshithijiyer]

For this, we need to add a self.info() or a popup on the UI?

[nworden]

I wouldn't want it to get blocked by popup blockers, so maybe we should display the warning directly on the page in place of the captcha, and have a button/link that users can click to load the captcha.