Loops and HTTP control server rework (#308)

- CRUD REST HTTP server
- `/v1` HTTP server prefix
- Retrocompatible with older routes (redirects to v1 or handles the requests directly)
- DNS, Updater and Openvpn refactored to have a REST-like state with new methods to change their states synchronously
- Openvpn, Unbound and Updater status, see #287

internal/server/wrappers.go

@@ -0,0 +1,32 @@
+package server
+
+import (
+	"fmt"
+
+	"github.com/qdm12/gluetun/internal/constants"
+	"github.com/qdm12/gluetun/internal/models"
+)
+
+type statusWrapper struct {
+	Status string `json:"status"`
+}
+
+func (sw *statusWrapper) getStatus() (status models.LoopStatus, err error) {
+	status = models.LoopStatus(sw.Status)
+	switch status {
+	case constants.Stopped, constants.Running:
+		return status, nil
+	default:
+		return "", fmt.Errorf(
+			"invalid status %q: possible values are: %s, %s",
+			sw.Status, constants.Stopped, constants.Running)
+	}
+}
+
+type portWrapper struct {
+	Port uint16 `json:"port"`
+}
+
+type outcomeWrapper struct {
+	Outcome string `json:"outcome"`
+}