Settings initializer

## Notes
- There are no default values besides the ones currently in the initializer file, so none of the settings can be removed.
- `strikes_for_ban` and `shelves` are not used in the application yet.
- The application must be restarted to change these settings (though you could theoretically change them at runtime with `rails console`).
- We might want to test changing the settings in our specs (especially since some settings share the same default values).