Allow only with cookie

[joeyhoer]

Would be nice to have a setting which would allow us to run this in prod – "Display only with cookie". Perhaps having a button in the backend "Get Cookie" & "Remove cookie".

[toddbc]

Potentially we could add that, but right now it uses the standard dev IP whitelist:

https://github.com/sdinteractive/SomethingDigital_CheckoutSuccess/blob/master/app/code/community/SomethingDigital/CheckoutSuccess/Model/Observer.php#L9

Which is the same as template hints, etc. I'd recommend adding the IP to the whitelist instead.

Otherwise, pull requests accepted.