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/internal/kvstore/kvstore_test.go

@@ -1,28 +0,0 @@
-package kvstore
-
-import "testing"
-
-func TestNoSuchKey(t *testing.T) {
-	kvs := NewMemoryKeyValueStore()
-	value, err := kvs.Get("nonexistent")
-	if err == nil {
-		t.Fatal("expected an error here")
-	}
-	if value != nil {
-		t.Fatal("expected empty string here")
-	}
-}
-
-func TestExistingKey(t *testing.T) {
-	kvs := NewMemoryKeyValueStore()
-	if err := kvs.Set("antani", []byte("mascetti")); err != nil {
-		t.Fatal(err)
-	}
-	value, err := kvs.Get("antani")
-	if err != nil {
-		t.Fatal(err)
-	}
-	if string(value) != "mascetti" {
-		t.Fatal("not the result we expected")
-	}
-}