Add elasticsearch-sql site

Add elasticsearch-sql site.
This is small web GUI client allowing you to make sql queries against the elasticsearch, showing results in a nice table instead of JSON.
To build zip file contains The elasticsearch-sql jar AND site use:
```
mvn assembly:single
```

unzip this file in plugins/sql will install both the site and the sql plugin.


if you upload this zip you can install the plugin with the site nicely:
```
bin/plugin -u http://URL/zipname.zip --install sql
```
You may consider upload the zip instead the current jar and fix the README accordingly.


The reason the additions is so big is libraries... bootstrap, jquery and codemirror.
The site itself is lightweight contains only 2 files: index.html, style.css

The 'Files changed' section take too much to load...
You can look at the changes at my fork: https://github.com/omershelef/elasticsearch-sql