Settings overhaul

The settings provided by the module are out-of-sync with the settings provided by the DAP JS. Over the years settings have been added and removed. We need to update the module to provide those offered by DAP v8.

While I'm at it, I really want to redesign the settings form. I want to simplify the library selection into a single radios element. All of the binary settings ought to be changed from true/false radios to checkboxes. And I want to add a status checkbox to enable/disable the module. The functionality is already in the module. It just isn't presented as an option to the admin.

Finally, I want to rewrite the configuration schema. All of the root-level settings retained their old, long D7 variable names. Functionally, they aren't hurting anything, but it makes for bad DX. I also want to flatten the schema a bit. This alone will force the release of version 3.0.0.