Simple java consumer

Creates a simple blocking java consumer.  It is expected that this code is executed inside of a thread (or something similar)


```ruby
# $bundle exec jruby hermann_test.rb


require 'hermann'
require 'hermann/provider/java_simple_consumer'
require 'hermann_jars'

zookeeper = "localhost:2181"
groupId   = "group1"
topic     = 'test'

example = Hermann::Provider::JavaSimpleConsumer.new(zookeeper, groupId, topic)

example.get_messages do |msg|
  puts "Recv: #{msg}"
end
```

I wanted to preserve the original API which takes in ```brokers, partition```.  Should we still support that?

Another thought would be to completely decouple Hermann::Consumer and JavaSimpleConsmer, (i.e. remove all code from here).  That way the users just declares the specific class they want.