Improves Editors and Grid controls.
Fixes
Editors for UWP (Windows 10)
- DateEdit causes a memory leak.
Grid for UWP (Windows 10)
- GridColumn's drag header elements don't disappear when holding and moving a column header on a touch screen.
- GridControl's context menu isn't shown when a column header is right-clicked on a tablet device.
- Provide the GridControl.CustomCellAppearance event.
