PropertyGrid and other things

[Changes]
 - Changed layout of main window.
 - Added tab view with property grid.
 - Brushes are now split into Anchors and Extensions in the Tree View.
 - Brushes no longer have children in the Tree View.
 - Brushes now show preview images of tiles in the Tree View.
 - Added Save As.. menu item.
 - JSON files are now saved when the entire package is saved.
 - Added Screenshot to the menu with its own Save As.. dialog.
 - Added Recent Files.. menu item.
 - The part that initially opens with the file will now show its selection in the tree view.
 - The brush selected by the eyedropper will be automatically selected in the tree view.
 - The editor no longer closes if a file cannot be opened.