winmain for winrt

WinRT passes the executable and Appx server info to the CRT main, and
supports several additional activation arguments as well. This handles the
arguments passed to main as well as the case where a modern app is
launched from an external application (e.g. Qt Creator).


Task-number: QTBUG-30198
Change-Id: Ia843e98c7843d5705f5f6d1c809de0b6bcdb5d26
Done-with: Kamil Trzcinski
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>