Added Support to add an Alias Record

[AltamashShaikh]

Hi,

I have added a support to add Alias Records for Route53(DB Upgrade version_20180508_upgrade.sql should be executed).

There was also one issue if we add cname for '@ ', this is not allowed in Route53 have added a validation check for it

I have tested the above changes and it works as intended, can you please review it and merge it accordingly

[jethrocarr]

Thanks for the PR @AltamashShaikh !

Looking at this code and how Route53 ALIAS records are handled, I believe this feature would break compatibility for other DNS servers such as Bind? So it works for users who are pure Route53, but will not allow for portability.

[AltamashShaikh]

what if I add a check for route53 only ?