Beta end sign up form

[xpaczka]

Issues connected

Ref #875 Ref #876
Resolves #878

What has been done

• Added logic for sign up form
• Added message for sign up form (success, failed, invalid email)

Testing

• [x] Entering no email - "Invalid email" message is displayed
• [x] Entering not valid email - "Invalid email" message is displayed
• [x] Entering valid email - "Sign up successful" message is displayed
• [x] If sign up successful, email input is cleared
• [x] All messages (success or fail) disappear after input change
• [x] After sign up, email used will be visible in customer.io -> People

Screenshots / images / videos

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[jagodarybacka]

Can we add a dot at the end of this sentence? we have dots everywhere else in this modal ah, and bellow is a typo