Added `size` option to percolate api

The `size` option in the percolate api will limit the number of matches being returned:
 ```bash
 curl -XGET 'localhost:9200/my-index/my-type/_percolate' -d '{
    "size" : 10,
    "doc" : {...}
 }'
 ```
 In the above request no more than 10 matches will be returned. The `count` field will still return the total number of matches the document matched with.

 The `size` option is not applicable for the count percolate api.

 Closes #3440