Bug fix in RenewCertificate Web Job, when using separate resource groups for App Service Plan and App Service

Fix for #56. The RenewCertificate code was not working when separate resource groups were used for App Service Plan and App Service.

Also added the option to specify when to renew the certificate. Add an AppSetting named RenewXNumberOfDaysBeforeExpiration and write the number of days before expiration of the certificate it should be renewed. It defaults to 14 days.