Changes Visual Studio Add-in 1.1

The Qt Visual Studio Add-In version 1.1.0 contains multiple bugfixes and
improvements.

Changes
-------
- The custom build step generation has been changed to use a subfolder for
  every configuration. This solves the problem of heavy changes in the vcproj
  file whenever the user switches to another build configuration. (Task 251918)
- Qt Designer, Qt Linguist and the QRC Editor are started via a properly
  registered editor wrapper. Now its possible to open ui files in other
  editors, like the built-in XML editor. (Task 250601)
- Projects can be converted from Qt Add-in projects to qmake generated
  projects and back. (Task 153484)
- Fixing the behaviour of adding a file to a filter. (Task 254968)
- Opening a vcproj file that has a non-defined Qt version works now like in
  the old Qt VS integration. (Task 258704)
- The detection of Windows CE Qt builds has been fixed.
- OpenGL Desktop Windows libraries aren't added to linker options in
  Windows CE projects. (Task 260550)
- If there's no Generated Files folder, then we don't try to delete its
  content. (Task 260723)
- Fix bug for solutions that contain disabled (unloaded) projects.
  (Task 259807)
- Switching between static and dynamic Qt builds has been fixed.
- Add-in's documentation has been updated.