Automatic start / restart of Kafka

This pull request aims to cover cases where one would like to either start Kafka if it's not currently running, or restart Kafka when a configuration file changes.

It currently considers the following "configuration" files, or the corresponding ones depending on which platform is used:

* `/opt/kafka/config/server.properties`
* `/opt/kafka/config/log4j.properties`
* `/etc/sysconfig/kafka`
* `/etc/init.d/kafka`

i.e. any configuration file that actively would effect running Kafka in any way.