Fix error "[9] System error: not a directory"

When starting the stack `with docker-compose up`, it gives out the error:

```
ERROR: Cannot start container e032695b38cdcd1c72597004f2369a7127b8233c9ecc2320c3b2bbd10209654b: [9] System error: not a directory
```

kibana is now executed using exec

kibana should be executed with exec to give it pid 1 and bind signal forwarding with the container instance

Close #19

Close #18

Updated logstash configuration. The elasticsearch output is now directly connected to the elasticsearch container.

Added a section about logstash memory configuration and logstash JMX remote access in the documentation.

Update README.md (small tweak)

updated readme file to include docker toolbox command

Updated project documentation.

Reviewed how configuration is managed for Kibana to be uniform for all components.

Use official images

Manages elasticsearch container using the latest official image inside this repository.
Manages the kibana container using the latest official image inside this repository.
Updated README.

Note about starting fig-elk when SELinux is enabled

Add a Gitter chat badge to README.md