Add indicator showing incorrect email provided

[prondzyn]

In current version of application we have green indicator onto attendee icon which indicates whether user provided an email during RSVP in Meetup - presence of the indicator means correct email was provided.

It would nice to have an yellow warning indicator showing when user provided any value but the value is incorrect. It could help catch some typos in user input. Ex. currently user can provide example@gmailcom (without a dot) email and we do not see anything - green indicator is absent. When we will have the warning indicator we can contact the person to log in and fix the typo.