Add support for VS 2017, fix various bugs

[vosen]

This PR does few things:

• Drops project.json in favour of packages.config
• Reorganizes project slightly (drops dead dependence on some internal MS libraries borrowed from RTVS)
• Resolves some issues with project loading (mostly runtime assembly load failures: eg. turns out, for assemblies *.DesignTime.dll you must always embed interop types)
• Adds support for VS2017. Only local debug works atm. AppVeyor and installers are next on the list.
• Upgrades ANTLR: targets for codegen of the version we used don't work with msbuild 15. I did the simplest thing and updated us to the newest prerelease version.

[briansmith]

it would be great to see the VS2017-compatible version on the Marketplace.