Removed support for aliases as part of index settings

Now that we have explicit support for aliases when creating indices and as part of index templates, we may remove support for aliases (only names) as part of index settings. This is partially breaking as the following calls:

curl -XPUT localhost:9200/index -d '{
  "settings" : {
    "aliases" : [ "alias1"]
  }
}

and

curl -XPUT localhost:9200/index -d '{
  "settings" : {
    "index.aliases" : [ "alias1"]
  }
}

were previously supported and will need to be replaced with

curl -XPUT localhost:9200/index -d '{
  "aliases" : {
    "alias1": {}
  }
}

Closes #5545
[TEST] check breaker reset after parent trip instead of trip count
Sort: Make `ignore_unmapped` work for cross-index queries.

Close #2255
Aggregations Added Filters aggregation

A multi-bucket aggregation where multiple filters can be defined (each filter defines a bucket). The buckets will collect all the documents that match their associated filter.

This aggregation can be very useful when one wants to compare analytics between different criterias. It can also be accomplished using multiple definitions of the single filter aggregation, but here, the user will only need to define the sub-aggregations only once.

Closes #6118