Currently the build without implicitly included precompiled header
is not supported anyway (because Qt MOC source files do not include
stdafx.h, they include plain headers).
So when we decide to support building without implicitly included
precompiled headers we'll have to fix all the headers anyway.
Some major platform-dependent file operations refactoring.
All methods like "open file", "open file with", "show in folder"
were moved to core/file_utilities module with platform-dependent
backends. All methods interacting with DesktopServices made async.
Now each platform-dependent module declares its interface in
platform/platform_module.h file and after that includes platform-
specific headers like platform/win/module_win.h with implementation.
Also removed the legacy WinRT platform-dependent implementations.
John Preston