Add extended ElasticSearch 7+ support and more flexibility to `elastic` lib

[cewald]

I've recently switched to ES7 and notices some incompatibilities in the API.

These are some proposals to have a more stable support for the current ES version and more flexibility:

• Remove type attribute from attribute/service/list method as it is already resolved by the adjustQuery depending on its version and will drop an ES exception if it is left in the search query
• Remove _updateQueryStringParameter method as it is unused as it is nowhere called
• Add getTotals method to elastic lib as from ES7 the totals return value is an object
• Add pingTimeout option and possibility for multiple ES hosts to elastic lib
• Use elasticsearch client library in catalog endpoint to make ES settings more consistent

I can make these changes for the storefront-api repo too if you wan't.

[cewald]

@andrzejewsky @gibkigonzo I've updated the branch – is this still under consideration or are any further changes necessary?

[cewald]

I've also adapted these changes for the storefront-api and would open a PR as soon as we are done here.