First draft of porting the preview to QML.

Already provides all features of the old preview + zooming.
Improve quick scene preview.

- Add overlay for highlighting item geometry
- Add ruler to measure sizes
- Allow redirection of input events
fix build
Fix small bug with the right ruler.

Ruler size was set to the scene's width instead of its height.
Make quick scene preview update correctly.

This commit adds a dependency to QtQuick 1.1 and thus on Qt 4.8.
Therefore the minimum required Qt version is raised to 4.8.0.
Fix two small issues with quick scene preview.

- Don't reset translation when a new frame arrives
- Correctly update image size when the frame size changes
Remove qDebug()s that existed only for development
Handle QtDeclarative correctly for both Qt major versions.
Fix Qt4 build, and make this argument a const reference.
Build with Qt 5.1.
Silence some compiler warnings and clean up includes.
Add license headers for quickitemoverlay.*
Add some comments to the QQ-scene preview QML code
Use decimal rgba notation in quickitemoverlay.

Qt4 doesn't seem to support the QColor("#aarrggbb") syntax, although
the docs say so. Now we're using the decimal based
QColor(rrr, ggg, bbb, aaa) instead, which does work.
Set default value for geometryData in quickpreview

This fixes a warning about not being able to assign undefined to a
QVariantHash. This commit also removes a few lines of dead code.