adding some functions to resolve ros message type

1. `Ros.getTopicType`
A wrapper of `/rosapi/topic_type`

2. `Ros.getMessageDetails`
A wrapper of `/rosapi/message_details`

3. `Ros.decodeTypeDefs`: adding a utility function to resoluve ros message definition
The function convert the result of `getMessageDetail` into a dictionary.
For example, `sensor_msgs/JointState` will be converted like:

```json
{
  "header": {
    "seq": "uint32",
    "stamp": "time",
    "frame_id": "string"
  },
  "name": [
    "string"
  ],
  "position": [
    "float64"
  ],
  "velocity": [
    "float64"
  ],
  "effort": [
    "float64"
  ]
}
```