Wizards: changes the structure of Wizards

This patch introduces platforms as a top level topic when choosing
a wizard. Also I changed the categories and priorities.

Details:

1. I did change the way the dialog/view is structured in newdialog.cpp

2. I added platformName() and supportsPlatform() to BaseQtVersion.
   I needed two functions because the Simulator does not provide a platform
   and therefore has no platformName but supports two platforms.
   I still have to turn the platform names into proper constants.

3. I changed the categories and priorities to get the layout that was
   discussed. (I had to touch quite alot of files but this is mostly trivial)

4. I added a combobox that allows filtering for platforms.

5. I added flags() to IWizard to indicate that a wizard is platform independent.

Change-Id: I86c7ad628a431ad06505c76580885c6e6c3ddc23
Reviewed-by: Alessandro Portale <alessandro.portale@nokia.com>