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/cmd/jafar/iptables/iptables_unsupported.go

@@ -0,0 +1,45 @@
+// +build !linux
+
+package iptables
+
+import "errors"
+
+type otherwiseShell struct{}
+
+func (*otherwiseShell) createChains() error {
+	return errors.New("not implemented")
+}
+func (*otherwiseShell) dropIfDestinationEquals(ip string) error {
+	return errors.New("not implemented")
+}
+func (*otherwiseShell) rstIfDestinationEqualsAndIsTCP(ip string) error {
+	return errors.New("not implemented")
+}
+func (*otherwiseShell) dropIfContainsKeywordHex(keyword string) error {
+	return errors.New("not implemented")
+}
+func (*otherwiseShell) dropIfContainsKeyword(keyword string) error {
+	return errors.New("not implemented")
+}
+func (*otherwiseShell) rstIfContainsKeywordHexAndIsTCP(keyword string) error {
+	return errors.New("not implemented")
+}
+func (*otherwiseShell) rstIfContainsKeywordAndIsTCP(keyword string) error {
+	return errors.New("not implemented")
+}
+func (*otherwiseShell) hijackDNS(address string) error {
+	return errors.New("not implemented")
+}
+func (*otherwiseShell) hijackHTTPS(address string) error {
+	return errors.New("not implemented")
+}
+func (*otherwiseShell) hijackHTTP(address string) error {
+	return errors.New("not implemented")
+}
+func (*otherwiseShell) waive() error {
+	return errors.New("not implemented")
+}
+
+func newShell() *otherwiseShell {
+	return &otherwiseShell{}
+}