Add more pre-defined download sources

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Currently we have only one source, would be great to have much more than one.

Furthermore I wish to make the download selection bit more programmatic and generic; Instead of hard-coding all the filenames on the remote server, we could write a "recursive selection" function that will finally yield a URL.

So to recap in my vision the optimal procedure is as follows:

• Command "download"
• Select from various hard-coded servers
• Recursive selection of a specific file
• Fetch the URL