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.


most of the additions is libraries: bootstrap, jquery and codemirror.
The site itself is lightweight contains only 2 files: index.html, style.css