Environment check before run

If gdk init/update/etc will can run system check (like go, ruby, postgres, etc versions) in the beginning, it would be very helpful.

For example:

Few days ago Go version was increased to 1.8, but before it was 1.6 and I had installed it. And after run gdk reconfigure/update I got unclear exception (...go-grpc-middleware/tags/context.go:3:8: cannot find package "context" in any of...). If gdk returned warning about wrong Go version, I would be more happy.

From #569 (closed):

Create a flexible system for checking software versions, starting with git v2.22 being required.