add skipUpdateStats option

[jagprog5]

Current use of the API:

// var rtManager artifactory.ArtifactoryServicesManager
// ...
// params
// ...
totalDownloaded, totalFailed, err := rtManager.DownloadFiles(params)

Doesn't expose skipUpdateStats=true

API example can be shown in this article:

GET http://localhost:8081/artifactory/libs-release-local/ch/qos/logback/logback-classic/0.9.9/logback-classic-0.9.9.jar?skipUpdateStats=true

I would not like to increment the download statistic when using the API and this functionality is currently missing ("skipUpdateStats" is not found anywhere in this project).

Thanks