Internal: Add some @Nullable annotations and fix related compilation warnings.

Added @Nullable to:
 - IndicesService.indexService
 - IndexService.shard
 - IndexService.shardInjector

This change doesn't try to do anything smart but just makes sure that a
*MissingException is thrown instead of a NullPointerException when the requested
object doesn't exist.

Close #7251
[TESTS] Make DisabledFieldDataFormatTests less evil.
function_score: fix explanation, [ was missing
[TEST] remove unneeded explain(true)

closes #7248
Fixed a typo
REST API: Allows all options for expand_wildcards parameter

This change means that the default settings for expand_wildcards are only applied if the expand_wildcards parameter is not specified rather than being set upfront. It also adds the none and all options to the parameter to allow the user to specify no expansion and expansion to all indexes (equivalent to 'open,closed')

Closes #7258
Analysis: Add keep_types for filtering by token type
Java api: fixed inconsistencies in PercolateRequest, added return type for method chaining where missing

Closes #7294
Merge pull request #7158 from uschindler/forbiddenapis-1.6-update

Update forbidden-apis to 1.6

Closes #7158
Add more logging for testSnapshotAndRestore backward compatibility test
Fixed a request headers bug in transport client

Where the configured request headers were not sent with sniffing requests (both node/info & cluster state sniffing)
Fix failed engine exception logging
Aggregations: Make the list of buckets for terms and histogram returned as a java.util.List.

The terms and histogram aggregations always have an order. So it would make the
response easier to consume to return the buckets as a list instead of a
collection in order to make it easier to do things like getting the first/last
buckets.

Close #7275
Build: Changed license header definition file xml encoding to UTF-8
[TEST] fix to wildcard_expansion tests to wait for green status
Mapping: Fixes using nested doc array with strict mapping

Closes #7304
Docs: Added Bloodhound Haskell client/DSL to docs

Closes #6031
Docs: Added tables for directory locations for deb+rpm and zip+tar.gz installs

Closes #6508
error in code

The top-tags and terms were reversed.
Typo