[ARM] Enable Standard SKUs for Load Balancers and PublicIPs

Microsoft introduced these improved new Standard LoadBalancers, with some interesting features and removing some limitations

https://docs.microsoft.com/en-us/azure/load-balancer/load-balancer-standard-overview 

For jclouds to use this we'd need to implement this new field SKU in the API 

https://docs.microsoft.com/en-us/rest/api/load-balancer/loadbalancers/get#loadbalancersku

However, to be able to use this Standard LBs we need to have also Standard SKUs for the publicIPs so the same would be needed in this API

https://docs.microsoft.com/en-us/rest/api/virtualnetwork/publicipaddresses/get#publicipaddresssku