organize essential APIs into platform, workflow and pkg folders (#337)

Add more logic to the way code is organized.

	/pkg -- library code not directly connected to micromdm
	/mdm -- packages meant for the services devices interract with. The MDM protocol.
	/dep -- DEP API and related packages.
	/platform -- Core APIs the server provides. Commands API, Devices API, queue, pubsub etc.
	/workflow -- Packages/API that build on top of platform. Today that's the webhook package.
		     Depending on what ends up here, the workflow folder might become its own repository.

platform/queue/command_queued.go

@@ -0,0 +1,34 @@
+package queue
+
+import (
+	"errors"
+
+	"github.com/gogo/protobuf/proto"
+	"github.com/micromdm/micromdm/platform/queue/internal/commandqueuedproto"
+)
+
+type QueueCommandQueued struct {
+	DeviceUDID  string
+	CommandUUID string
+}
+
+func MarshalQueuedCommand(cq *QueueCommandQueued) ([]byte, error) {
+	if cq == nil {
+		return nil, errors.New("marshalling nil QueueCommandQueued")
+	}
+	return proto.Marshal(&commandqueued.CommandQueued{
+		DeviceUdid:  cq.DeviceUDID,
+		CommandUuid: cq.DeviceUDID,
+	})
+}
+
+func UnmarshalQueuedCommand(data []byte) (*QueueCommandQueued, error) {
+	cmdQueued := commandqueued.CommandQueued{}
+	if err := proto.Unmarshal(data, &cmdQueued); err != nil {
+		return nil, err
+	}
+	queueCmdQueued := new(QueueCommandQueued)
+	queueCmdQueued.DeviceUDID = cmdQueued.DeviceUdid
+	queueCmdQueued.CommandUUID = cmdQueued.CommandUuid
+	return queueCmdQueued, nil
+}