refactor: move more commands to internal/cmd (#207)

* refactor: move more commands to internal/cmd

Part of https://github.com/ooni/probe/issues/1335.

We would like all commands to be at the same level of engine
rather than inside engine (now that we can do it).

* fix: update .gitignore

* refactor: also move jafar outside engine

* We should be good now?

internal/engine/cmd/oohelperd/oohelperd_test.go

@@ -1,15 +0,0 @@
-package main
-
-import (
-	"testing"
-)
-
-func TestSmoke(t *testing.T) {
-	// Just check whether we can start and then tear down the server, so
-	// we have coverage of this code and when we see that some lines aren't
-	// covered we know these are genuine places where we're not testing
-	// the code rather than just places like this simple main.
-	go testableMain()
-	srvcancel()  // kills the listener
-	srvwg.Wait() // joined
-}