Fix & cleanup whitespace in qquickdrag.cpp docs

Change-Id: I85b986c8b3dca6ccc872807a1d2e8b7b71688c0e
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Docs: fix Drag::onDragStarted() and onDragFinished() signals

Change-Id: Iefda2d3611ed0f940255f1375ca4c356827fbc70
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
QtQuick window example improvements: window size and DPI info

On high-resolution displays it's important to size the window so that
the content will fit.  Also show the DPI conversion for pixel density.

Change-Id: Ie35852ecff0bb0ee5ab9b77c6c18e82cfc300448
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>