test protos in /tests/proto2js/Tests/ for testing imports

These three protos will demonstrate/test imports.  Note that the current imports with proto2js don't quite work. Here's what this protojs command
```
node proto2js ..\tests\proto2js\Tests\MediaDevice.proto -path=..\tests\proto2js
```

with this in MediaDevice.proto:
```
import "Tests/MediaPlayer.proto";
import "Tests/ZmqMediaPlayer.proto";
```

generates

```
{
    "package": null,
    "messages": [
        {
            "name": "MediaDevicePbm",
            "fields": [
                {
                    "rule": "optional",
                    "type": "bool",
                    "name": "auto_play",
                    "id": 1,
                    "options": {}
                },
                {
                    "rule": "optional",
                    "type": "MediaPlayerPbm",
                    "name": "media_player",
                    "id": 30,
                    "options": {}
                },
                {
                    "rule": "optional",
                    "type": "ZmqMediaPlayerPbm",
                    "name": "zmq_media_player",
                    "id": 31,
                    "options": {}
                }
            ],
            "enums": [],
            "messages": [],
            "options": {}
        }
    ],
    "enums": [],
    "imports": [
        {
            "package": null,
            "messages": [
                {
                    "name": "ZmqMediaPlayerPbm",
                    "fields": [
                        {
                            "rule": "optional",
                            "type": "bool",
                            "name": "test",
                            "id": 1,
                            "options": {}
                        }
                    ],
                    "enums": [],
                    "messages": [
                        {
                            "ref": "MediaPlayerPbm",
                            "fields": [
                                {
                                    "rule": "optional",
                                    "type": "ZmqMediaPlayerPbm",
                                    "name": "zmq_media_player",
                                    "id": 310,
                                    "options": {}
                                }
                            ]
                        }
                    ],
                    "options": {}
                }
            ],
            "enums": [],
            "imports": [
                "Tests/MediaPlayer.proto"
            ],
            "options": {},
            "services": []
        },
        "Tests/ZmqMediaPlayer.proto"
    ],
    "options": {},
    "services": []
}
```

Unfortunately,  "Tests/MediaPlayer.proto" fails to get imported TWICE. It should be in both the MediaDevice message and the ZmqMediaPlayer (unless you avoid duplication, which I think the code does try to do). Also "Tests/ZmqMediaPlayer.proto" remains listed as an import, even though it already has been turned into JSON.