I need a way of reseting darktable to its factory settings.
With shotwell it is simply a case of deleting the home directory for shotwell, but there doesn't appear to be one for DT under the Darktable name.
I believe that the config files for darktable are under ~/.config/darktable. Usually, deleting the config files will cause them to be regenerated at the next startup. Any changes you made to the default settings will be lost.
Before deleting your config files, though, delete just the Darktable library file (~/.config/darktable/library.db). This is where Darktable saves information about the images you've imported. After you delete the library file, Darktable won't know anything about your image collection (and should stop crashing). You'll have to re-import the photos you want to work with, but happily, the library file is mostly just a cache that speeds up various operations within Darktable. Darktable saves all important image metadata (including tags, edit history, etc.) in XMP "sidecar" files alongside the images themselves. Hopefully, all you'll lose is a bit of time.
Always make a backup of any files you intend to experiment with.