Introducing kpm build

- Moved k build to kpm build
- Kept k build around (referencing Microsoft.Framework.Project now references Microsoft.Framework.PackageManager) to make the transition smoother
- Made kpm run on core clr (kpm restore still doesn't work)
- Removed check
Probably this doesn't matter anyways. kpm only needs to work enough for build since it was moved. The rest of it just needs to be fixed