- Add the option to discover devices
- Clear the model when a new discovery is started. In the previous implementation the model was only cleared if new data was available.
This can lead to some funny results.
- Change some property types to enums
- Enhance the qmlscanner example

Change-Id: I94f33e3eabd7440b5c0c6c83f3e8158009bd2dbd
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>