MSBuildTools selection is a mess

Now with VS2017 out, the code for the detection of the correct MSBuildTools installation is a total mess and works just by accident.

Things to do:

• Give more output that can help understand what is going on Done via PR 255
• Give more ways to understand selection Done via PR 259
• Integrate new restrictions like no Win8.1 support with VS2017-only installations Acceptable limitation for a dead platform I think
• Simplify selection code that is currently spread over 2 files: `MSBuildTools.js` and `build.js` Done via PR 259