C++: Start rewriting dwtest in C++ as dwtestoo. Only the lambda version currently, so will break on old compilers. Only the main window and first page is implemented so far but... the first page works on MacOS at least. Fill in some missing pieces I ran into while porting dwtest to C++.

[Desktop Entry]
Name=Dynamic Windows Test
Exec=@prefix@/bin/dwtest 
Terminal=false
MultipleArgs=false
Type=Application
Categories=Application;Development;X-Red-Hat-Base;