Custom & system user-agent support.
I'm not sure as to what API the System.getProperty("http.agent"); exists from and I can't seem to find any details, so I made it so that it'll try for the systems user-agent, if that's null it'll use the backup that you've provided (default blank). I plan on adding error support for if ultimately no user-agent is found, could also fall back to the default user-agent that's provided from Apache. Additionally an option to force your custom user-agent has been added.
More work towards MtGox integration has also been done, you're able to select the currency, the connection is established, the data is fetched but nothing is done with the data as of yet. Not sure how to handle errors for that as of yet.