[DOCS] Javadoc: delete index request does not support empty String

In 0.90.x I was able to delete all my indices from the java api by calling

    client.admin().indices().prepareDelete(new String[] {}).execute().actionGet();

However this fails in 1.0.0 with

org.elasticsearch.action.ActionRequestValidationException: Validation Failed: 1: index / indices is missing;
	at org.elasticsearch.action.ValidateActions.addValidationError(ValidateActions.java:29)
	at org.elasticsearch.action.admin.indices.delete.DeleteIndexRequest.validate(DeleteIndexRequest.java:72)
	*snip long stacktrace*

which points me to

    public ActionRequestValidationException validate() {
        ActionRequestValidationException validationException = null;
        if (indices == null || indices.length == 0) {
            validationException = addValidationError("index / indices is missing", validationException);
        }
        return validationException;
    }

So that's what now throws the error, however the documentation still says:

    /**
     * Deletes an index based on the index name.
     *
     * @param indices The indices to delete. Empty array to delete all indices.
     */
    DeleteIndexRequestBuilder prepareDelete(String... indices);

Closes #5164.
Closes #5167.
Closes #5168.
Fix SearchContext from being closed prematurely

Fixes SearchContext from being closed during initialization or immediately
after processing is started

Closes #5165
Add test and randomization for #5165
Alias code cleanup

- Renamed IndexMetaData#removerAlias to removeAlias
- Removed IndexTemplateMetaData#fromXContentStandalone unused method (relates to #4511)
- MetaDataIndexAliasesService fix typo in comment
- Alias removed unused constructor that accepts both alias name and filter
[TEST] Added tests for alias filter that is valid json but not a valid filter
Added script to extract release notes

Just call ./es_release_notes.pl <issue-tag> to get all release notes.

By default html output is returned, but you can switch to markdown by calling
./es_release_notes.pl <issue-tag> markdown
[DOCS] Fixed typo in create index api
[TEST] Initialization errors are checked before returning "no tests to run" error

If there initialization errors and no tests to execute at the same time, better to return the initialization errors, whose check should be first then, as it might be that the "no tests to execute" is caused by the initialization errors.
Added tests for empty token chars on ngram tokenizer

This relates to #5120
[TEST] Added index templates tests for broken mapping and invalid settings scenarios
[TEST] Update testNGramCopyField to reflect the effect of an index_analyzer
Make _exists_/_missing_ behave consistently with exists/missing.

`_exists_` and `_missing_` miss field name expansion that `exists` and
`missing` have, which allows these filters to work on `object` fields.

Close #5142
Add mustache templating to query execution.

Adds support for storing mustache based query templates that can later be filled
with query parameter values at execution time. Templates may be both quoted,
non-quoted and referencing templates stored in config/scripts/*.mustache by file
name.

See docs/reference/query-dsl/queries/template-query.asciidoc for templating
examples.

Implementation detail: mustache itself is being shaded as it depends directly on
guava - so having it marked optional but included in the final distribution
raises chances of version conflicts downstream.

Fixes #4879
Fixing license headers.
[TEST] Added whitespaces after brackets, colons and commas in nested percolator test.
The seed format is suite:method, clarified it in the docs.
[DOCS] Included the `_percolator` index breaking change to migration docs.
[TEST] Removed whitespace between } and ,
Wait for REST Service to start

When running tests for site plugins, it could happen that the REST Service is not fully started and not ready immediately to serve HTTP requests.
It gives `503 Service Unavailable` error in that case.

This patch will gives 5 seconds before failing the test.
Add thrid party license generation profile