Elasticsearch Connector Views integration

When using Contextual filters the ArgumentPluginBase add the field with the table alias even if no alias is used, resulting in a "." fieldname

Added code to replace "." to ""

@ralphvdhoudt I see a removed file in the interdiff of #19. Was it intentional?

I made a side patch (i.e. use it on top of the base patch you are using) which fixes a bug about the date field views plugin, especially when a non timestamp value is indexed (like strict_date_optional_time). When not using this patch, views fails to render the results when a non timestamp date is offered to the views plugin.

The patch worked on 8.x-7.0-alpha3 with the #13 base patch (it should work on other base patches).

The attached patch is the #18 + the patch #19 made compatible with PHP7 (replaced str_starts_with with strpos).

This one contains the fixes from #21 about the timestamp fields.

This one is a fix over the field deduplication during the query building. Before, the deduplication resulted in ES returning an error about invalid string key. This happens when two fields of the same "source field" are retrieved, and only when they are not placed at the end of the field list, causing a "hole" in the index: key 0, key 1, key 2, key 4.

By reindexing the array, it makes the query work again.

the patch in #22 do not work with 8.x-7.0-alpha5