Speed up string sort with custom missing value

Today if the user supplies a custom missing value for a string sort,
we do it in an extremely slow way, not using ordinals but dereferencing
bytes for every document. Ordinals are only used if the missing value
is _first or _last.

Instead, use ordinals with custom missing values too.

Closes #7005
Aggregations: Better JSON output scoping

Before this change each aggregation had to output an object field with its name and write its JSON inside that object.  This allowed for badly behaved aggregations which could write JSON content in the root of the 'aggs' object.  this change move the writing of the aggregation name to a level above the aggregation itself, ensuring that aggregations can only write within there own scope in the JSON output.

Closes #7004
[Benchmark] Make TermsAggregationSearchBenchmark fairer to uninverted field data.

The benchmark indexes 200 unique full-width longs. For uninverted field data
we try to use the most memory-efficient storage, and in that case it would use
two arrays: one for the doc->ordinals mapping and one for the ordinal->value
mapping. Which is slower than what doc values do by storing directly the
mapping from docs to values.
Internal: expose the indices names every action relates to if applicable

Added two new interfaces:
1) IndicesRequest that allows to retrieve the indices the request relates to in a generic manner, together with the indices options that tell how they are going to get resolved and expanded
2) CompositeIndicesRequest for compound requests that hold multiple indices request like MultiSearchRequest, MultiGetRequest, MultiTermVectorsRequest, BulkRequest, BenchmarkRequest, PercolateRequest, MultiPercolateRequest and MoreLikeThisRequest

Taken the chance to streamline the indices options and add them to every request where it makes sense (although they can't be changed from the outside), rather than leaving them implicit in the related TransportAction when indices get expanded (tipycally MetaData#concreteIndices or MetaData#concreteSingleIndex). Added IndicesOptions parameter to MetaData#concreteSingleIndex to make sure it is taken from the request, where the information belongs, instead of hardcoded within MetaData. The concreteSingleIndex method remains but it's just a utility method that returns a single index instead of an array and complains otherwise.

Also made sure NPE is never thrown when setting indices(null) to IndicesAliasesRequest, similar to what SearchRequest does.

Closes #6933
remove use of recycled set in filters eviction
closes #7012
[TESTS] Ensure yellow in SimpleFacetsTests.testFilterFacetWithFacetFilterPostMode.
Aggregations: Added pre and post offset to histogram aggregation

Added preOffset and postOffset parameters to the API for the histogram aggregation which work in the same way as in the date histogram

Closes #6605
Add `wait_if_ongoing` option to _flush requests

This commit adds the ability to force blocking on the flush operaition
to make sure all files have been written and synced to disk. Without
this option a flush might be executing at the same time causing the
current flush to fail and return before all files being synced.

Closes #6996
Geo: Fixes parse error with complex shapes

The bug reproduces when the point under test for the placement of the hole of the polygon has an x coordinate which only intersects with the ends of edges in the main polygon. The previous code threw out these cases as not relevant but an intersect at 1.0 of the distance from the start to the end of an edge is just as valid as an intersect at any other point along the edge.  The fix corrects this and adds a test.

Closes #5773
Core: Use the provided cluster state instead of fetching a new cluster state from cluster service.

Close #7013
Add a periodic cleanup thread for IndexFieldCache caches

Fixes #7010
Fielddata: Fix thread safety issue with field data on the `_index` field.
[TEST] more logging
[TESTS] Fix NPE in FreqTermsEnumTests.
Tests: Remove HttpClient to only use one Http client

The HTTP client implementation used by the Elasticsearch REST tests is
backed by apache http client instead of a self written helper class,
that uses HttpUrlConnection. This commit removes the old simple HttpClient
class and uses the more powerful and reliable one for all tests.

It also fixes a minor bug, that when sending a 301 redirect, a Location
header needs to be added as well, which was uncovered by the switching
to the new client.

Closes #7003
[DOCS] correct documentation about groovy/mvel defaults and deprecations
CORS: Support regular expressions for origin to match against

This commit adds regular expression support for the allow-origin
header depending on the value of the request `Origin` header.

The existing HttpRequestBuilder is also extended to support the
OPTIONS HTTP method.

Relates #5601
Closes #6891
Docs: Added new entry for the SIREn plugin.

Closes #6961
Docs: Changing ES_MAX_MEM default from '1gb' to '1g'

If you set ES_HEAP_SIZE to '1gb' as suggested, Java will yield an "Invalid initial heap size".

Closes #6824
Aggregations: Added an option to show the upper bound of the error for the terms aggregation.

This is only applicable when the order is set to _count.  The upper bound of the error in the doc count is calculated by summing the doc count of the last term on each shard which did not return the term.  The implementation calculates the error by summing the doc count for the last term on each shard for which the term IS returned and then subtracts this value from the sum of the doc counts for the last term from ALL shards.

Closes #6696