Improved alternate DataGrabber interface

This alternate approach to the DataGrabber uses the {}-based string format syntax instead of the %-based syntax of the previous version. Because it is totally backwards incompatible with the original DataGrabber, I wrote it as as second class.

Please don't merge with the `DataGrabber2` name, that is just a placeholder. Suggestions for other names are welcome. We could go with a name that distinguishes it from DataGrabber (e.g. `FormatGrabber`, although that doesn't make a lot of sense), or just a synonym (e.g. `SelectFiles`). I'd probably lead towards the latter.

I think this approach should cover (at least) as many use cases as the existing DataGrabber, but please let me know if there's something obvious I've left out.