Motion events endpoint

### Motion Events
Detected motion events.

#### Register motion `POST` `/v1/motion_event`

**Request body**

```json
{
  "user" : "authorized-user",
  "password" : "user-password",
  "title" : "motion",
  "categories" : ["Sensor 1", "December 17th, 2014 at 03:41AM"]
}
```

**Response**

A `HTTP 201 Created` with body:

```json
{
  "_id": "5230b76440823cd634000001",
  "sensor_name": "Sensor 1",
  "state": "motion",
  "date_modified" : "2013-09-11T18:46:16.472Z",
  "date_created" : "2013-09-11T18:32:31.147Z"
}
```