[SPARK-2788] [STREAMING] Add location filtering to Twitter streams

TwitterUtils.createStream(...) allows users to specify keywords that restrict the tweets that are returned. This change adds a location parameter that also restricts the returned tweets.
Rather than changing this signature and adding another one (the above one), it probably better (in terms binary compatibility) to add a single new method, that is 
```
def createStream(
      jssc: JavaStreamingContext,
      twitterAuth: Authorization,
      filters: Array[String],
      locations: Array[Array[Double]],
      storageLevel: StorageLevel
    ): JavaReceiverInputDStream[Status] = {
```

Same applies to the Scala API.