Provide mechanism for reading database lists from inside a zip file and a mechanism to download them

The filelist databases interfaces are excellent but I think we're lacking two features:

• Reading the filelists from inside a zip file (to save space).
• Automatic downloading of these filelists and saving them in e.g. ~/.bob for convenience.

I don't think these file lists should be checked into the source code and I think they should be managed the same way as we handle deep learning models.