Automate the conversion of whole solutions to Qt VS Tools

The conversion of VC++ projects to the Qt VS Tools format may take up to a few minutes when converting very big projects. This is compounded by the fact that it's only possible to convert one project at a time. It should be possible to automate the conversion of entire solutions / batches of projects without the need for user intervention.

Project format conversion should also include upgrading from previous Qt/VS project formats, namely custom build based projects, referencing both Qt5 and Qt4, and also Qt/MSBuild projects with outdated format version.