Feature: Add support for `nested` object mapping

**Issue Type:**

Enhancement

**Platform:**

ReactiveSearch for Web

**Description:**

ReactiveSearch today doesn't support querying the fields of an object field with a [nested mapping](https://www.elastic.co/guide/en/elasticsearch/reference/6.4/nested.html).

A nested object requires a different query (where a path for the nested field needs to be specified) along with the original query. The same applies to an aggregation.

This issue proposes to add a `nestedField` prop in all the data-driven components we have to support the use-case of a nested object.

Prop definition for the field looks like:

**nestedField** `String` [optional]
When your dataField is present inside an object of type [`nested`](https://www.elastic.co/guide/en/elasticsearch/reference/6.4/nested.html), this can be used to set the path of the nested field. Setting this allows searching within documents belonging to the path.

**Reactivesearch version:** x.y.z

2.12.1

Components to support this in:

- [x] MultiDropdownList
- [x] SingleDropdownList
- [x] MultiList
- [x] SingleList
- [ ] SingleRange
- [ ] MultiRange
- [ ] SingleDropdownRange
- [ ] MultiDropdownRange
- [ ] DataSearch
- [ ] CategorySearch
- [ ] TextField
- [ ] ToggleButton
- [ ] TagCloud
- [ ] SingleDataList
- [ ] MultiDataList
- [ ] RangeSlider
- [ ] DynamicRangeSlider
- [ ] RangeInput
- [ ] NumberBox
- [ ] DatePicker
- [ ] DateRange
- [ ] RatingsFilter
- [ ] GeoDistanceSlider
- [ ] GeoDistanceDropdown