Provide option for document title feature filter

[martindholmes]

I was just thinking about configuring a feature filter for document titles, and it occurred to me that we already have all the info we need to construct one in the titles_x.json file, so it would be very wasteful to have to generate and download another. Why don't we make it just a config option to create that filter automatically?

[joeytakeda]

I now realize I had never replied to this! I think that's a good idea and one that would be quite helpful, so no objections here. I'm going to put this to Blue Sky for now since the 2.0 milestone is getting a bit crowded, but feel free to move it to 2.0 if you need this urgently.