Logs a registered member in with an email and password.
The login() function returns a Promise that resolves to a session token
used to log a member in to your site.
The login() function only works with existing members. To register a new member use
the register() function.
To complete the login,
the returned session token must be applied using the
applySessionToken()
function (from wix-members-frontend) in page code.
Login email address.
Member password.