Called when downloading content from Steam workshop begins. Used by default to show fancy workshop downloading panel.

The order of Workshop hooks is this:

• WorkshopStart
• WorkshopDownloadTotals
• • These are called for each new item:
• WorkshopDownloadFile
• WorkshopDownloadProgress - This is called until the file is finished
• WorkshopDownloadedFile
• WorkshopEnd (this ones called once)