Not working on higher versions of Java ( > 8)

[theovier]

Better late than never. As Java 9 introduces some new features, I realized the downloader is not working correctly with higher Java versions. The program needs to be restructured in order to reflect the changes Java 9 introduced as otherwise, the downloader won't start. If you want to use it, make sure you are executing it in a Java 8 environment.
If someone wants to propose a fix for this, feel free to start a pull request. Unfortunately, I don't have the time for it now.