[Development] Qt 5.9

[Maurice Kalinowski]

> > - For WinRT/WinPhone I propose to drop WinRT 8.1 and WinPhone 8.1
> support & start using term UWP (Universal Windows platform).  It means also
> dropping msvc 2013 from WinRT/WinPhone; UWP only supports msvc2015
> 
> Absolutely agree.
[Kalinowski Maurice] 
Start using the term UWP in our website etc. WinRT is still a technical correct term for the API. So we should not start simply renaming mkspecs or such.

In addition this causes a couple of changes to our CI system. My proposal would be:

- Have winrt-x86-msvc2015 (or winrt-x64-msvc2015) replace the winphone-arm-msvc2013 test target on CI. Right now this would be the same build test, but I still hope that CI resources will allow regular CI auto tests at one point
- Have winrt-arm-msvc2015 replace winrt-x86-msvc2015 replace to be tested during qt5.git integration. Currently Windows 10 (UWP) is only tested for the integration due to resource constraints. It should not get worse when we are removing platforms.

BR,
Maurice