Various desktop icon fixes
Bundle of patches that should help improve the desktop icon positioner and avoid random icon movements.
- FolderView was out of sync with the Positioner movements: It calculated it's own perStripe value and had off-by-one error in the for loop
- FolderModel would move icons even when screen was not in use, causing useless calculations to happen.
- FolderItemDelegate would constantly warn about an undefined model, so fixed it
- Added couple comments to Positioner because those parts would be hard to understand otherwise
- Refactor positioners "updateResolution" a bit, to avoid doing unnecessary work: We just want to know what the resolution is, not do everything related to it, since different places of code handle this differently.
- In folderModel, clear the dropTargetPositions after dragging icons around on the desktop. Otherwise it would get reused by any rowInserted signal. There is a 10 second timer to clear it, but we should not rely on that.
Edited by Akseli Lahtinen