Storage sas commands and set/get service properties

1. Set-AzureStorageServiceLogging/Set-AzureStorageServiceMetrics
2. Get-AzureStorageServiceLogging/Get-AzureStorageServiceMetrics
3. New-AzureStorageContainerSasToken, New-AzureStorageBlobSasToken, New-AzureStorageTableSasToken, New-AzureStorageQueueSasToken,
4. New-AzureStorageContext with sas token.