Fixing the neo4j:install rake task for systems without wget and Windows

Fixes #62

On non-Windows systems like Mac OS X where wget isn't installed out of the box, the ```rake neo4j:install``` task fails. This PR fixes that issue by using HTTParty to replace the wget command to fetch the neo4j tar.gz

Also, there was another issue on Windows systems that found out while testing the fix for the issue above, in which the rake task wouldn't run on Windows systems - failing due to the fact that HTTParty was not required, and also the Zip gem which is used in the task to extract the downloaded zip file, wasn't included in the Gemfile itself.

Lastly, the neo4j.zip file which was downloaded was not being removed from the filesystem the way it is done on non-Windows systems