Docs: Added new elasticsearch-river-kafka plugin to the documentation (uses latest version of Kafka, EL Bulk API, and supports concurrent requests)

Closes #8518
Docs: Remove reference to imaginary "no_docs_query"

No reference to it in the source code except this file.

Closes #8566
Fix error in documentation

Indexation does not fail if no timestamp provided when there is a default value defined in mapping.
Missing quote in the example
Docs: Update update-settings.asciidoc

Inconsistent indentation

Closes #8525
Core: Fix script fields to be returned as a multivalued field when they produce a list.

This change is essentially the same as #3015 but on script fields.

Close #8592
Switch to forbidden-apis 1.7
Core: upgrade to current Lucene 5.0.0 snapshot

Elasticsearch no longer unlocks the Lucene index on startup (this was
dangerous, and could possibly lead to corruption).

Added the new serbian_normalization TokenFilter from Lucene.

NoLockFactory is no longer supported (index.store.fs.fs_lock = none),
and if you have a typo in your fs_lock you'll now hit a StoreException
instead of silently using NoLockFactory.

Closes #8588
Docs: Update plugins.asciidoc on river plugins section

Adding links to Amazon S3 and Google Drive river plugins

Closes #8544
Docs: Reword note regarding _source for accuracy

Previously it suggested _source was always present, when that is not the case.

Closes #8491
Remove NoneGateway, NoneGatewayAllocator, & NoneGatewayModule

Always use the LocalGateway* equivalents

We already check in the LocalGateway whether a node is a client node, or
is not master-eligible, and skip writing the state there. This allows us
to remove this code that was previously used only for tribe nodes (which
are not master eligible anyway and wouldn't write state) and in
tests (which can shake more bugs out)
[TRANSLOG] Cut over to Path API