Button to enumerate devices, ability to set and unset BaseItem:pulse, initial scaffolding for a separate type for device items
It's now possible to set BaseItem:pulse to something other than FALSE. Once set GdMainIconBoxChild will show a spinner. This will be used while content is being imported from a device and added to a local collection.
Device items will have a different thumbnail cache, which makes it necessary to have a separate sub-class. Some ItemManager scaffolding to make that possible.
This is another step towards #29 (closed).