Support other platform names on configure.exe

Support other platform names on configure.exe

Added three new methods, which are meant to be used internally to
configureapp.cpp:
    - int platform(): returns an integer representing a platform
    - QString platformName(): returns the platform name string to be used when
      displaying the license agreement.
    - QString qpaPlatformName(): returns the value to be defined as
      QT_QPA_DEFAULT_PLATFORM_NAME.

Currently supported names are Windows, Windows CE, QNX and Blackberry. Default
is "Windows".

Change-Id: Ifa4d1b9c02cda956be9becdf8db195d3d494f1d5
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>