Ensure we use local installed MsBuild

[dfev77]

Use MSBuildLocator to load the local installed MsBuild and do not distribute the compile type referenced MsBuild libs. This is needed in order to avoid using older MsBuild versions from GAC as new VS versions don't install assemblies in GAC.

Notes:

• Works only with VS 2017 and later!
• Had to manually remove the props & targets files included by the Locator package due to backward compatibility with msbuild (see https://github.com/Microsoft/MSBuildLocator/issues/52)
• tests are not using locator as AppVeyor is building using MsBuild 14, so using locator would fail the tests there