Add Dev14 support

Also remove incorrect copy local.

The solution should now build and install on VS 11, 12, and 14, and the build from any version should work on any other version.
These are only needed in VS extension projects; the VS extension project type will automatically add a `<MinimumVisualStudioVersion>` for the current version.  (I have no idea why they do that)

@JaredPar invented this trick to bypass the restriction.