Remove Lucene's deprecated PatternTokenizer

Instead of using the PatternTokenizer, the functionality was replicated by using Lucene's StopFilter, PatterTokenizer and LowerCaseFilter

Closes #6717
Improve Settings#get lookup for camel case support
Today, if we miss on a get on setting, we try its camel case version. The assumption is that in our code, we never use camel case to lookup a setting, but we want to support camel case if the user provided one.
This can be expensive (#toCamelCase) when the get on the setting is done in a tight call, which is evident when running the allocation deciders as part of the reroute logic.
Instead of doing the camel case check on get, prepare an additional map that includes all the settings that are provided as came case, and try and lookup from it if needed.
closes #6765
Add v1.2.3 to Version.java
Fix typo in Hunspell logging
Docs: Update plugins.asciidoc

Closes #6683
Docs: New entry/front-end

Adding, Calaca, a simple search client for Elasticsearch.

Closes #6754
[Test] BackgroundIndexer uses the wrong logger

Closes #6781
Merge pull request #6792 from areek/fix/6717

Remove Lucene's deprecated PatternAnalyzer
Upgrade to jackson core 2.4.1.1
Note, we had to disable the symbol overflow, since the many mapping case was tripping it
closes #6789
Modify command window title (windows)

When launching multiple nodes in MS Windows env, batch command window does not come by default with any title.

This patch add `Elasticsearch VERSION` as a title, where VERSION is the current elasticsearch version.

Same for `plugin.bat` and `service.bat`.

Closes #6336
Closes #6752