gui: ImagesTreeView: optimizations
gui: ImagesTreeView: code cleanup
gui: ImagesTreeView: do not use PositionsCalculator on an empty model.

Reason is different than it may look: when first, empty model is set,
Data may not contain configuration yet which leads to crash
gui: ImagesTreeView: Data: turning off dump()
gui: PositionsCalculator: take margins into account when calculating items per row
VisualStudio build fixes
gui: PositionsCalculator: enabling size calculations for root item.

This will allow to calculate size of all items
gui: ImagesTreeView: scrollbars update
gui: PositionsReseter: invalidateItemOverallRect: allowing reset of root object
gui: code cleanup
gui: PositionsCalculator: fixing problem with root's overallSize
gui: ImagesTreeView: fixing issues related to proper offset calculation
gui: Introducing TreeItemDelegate
gui: Data: removing QAbstractItemModel from getImage() & isImage()
gui: ImagesTreeView: moving painting code to delegate
gui: PositionsReseter: itemChanged() introduced; fix for not reseted children when parent is reseted
gui: ImagesTreeView: reset item when it is colapsed or expanded
gui: PositionsCalculator: fixing margins
gui: TreeItemDelegate: basic implementation
gui: ImagesTreeView: QStyleOptionViewItem for delegate filled