Added multi percolate api

The multi percolate allows the bundle multiple percolate requests into one request. This api works similar to the multi search api. The request body format is line based. Each percolate request item takes two lines, the first line is the header and the second line is the body.

The header can contain any parameter that normally would be set via the request path or query string parameters. There are several percolate actions, because there are multiple types of percolate requests:
* `percolate` - Action for defining a regular percolate request.
* `count_percolate` - Action for defining a count percolate request.
* `percolate_existing_doc` - Action for defining a percolate existing document request.
* `count_percolate_existing_doc` - Action for defining a count percolate existing document request.

Each action has its own set of parameters that need to be specified in the percolate action.
Format:
```
{"[header_type]" : {[options...]}
{[body]}
```

Depending on the percolate action different parameters can be specified. For example the percolate and percolate existing document actions support different parameters.

The following endpoints are supported:
```
POST localhost:9200/[index]/[type]/_mpercolate
POST localhost:9200/[index]/_mpercolate
POST localhost:9200/_mpercolate
```

The `index` and `type` defined in the url path are the default index and type.

Closes #3488