This fixes thumbnailing for XDG desktops. The new script doesn't depend on GNOME libs and works either with python3 or python2.
Also, a thumbnailer config file is added to the installation in CMakeList.txt
If the tp_print slot is not set the warning -Wmissing-field-initializers is raised. If it's set then -Wdeprecated-declarations is raised.
So, the only way is to suppress it.
This single files does not help anything, one would also need the *.vcxproj files. But whatever I try, unless you run not CMake prior to compiling, it will try to build a Win32 DLL and fails.
So since I cannot find a way to provide .sln and .vcxproj files that can be used out of the box, the single .sln file is just senseless alone.
On Windows, the python script opens a file with the default ANSI
encoding. This causes UnicodeDecodeError in some region. The encoding
should be set explicitly to match the files.