Get rid of snappconfig

[werebus]

And our ApplicationConfiguration wrapper. That gem hasn't been updated in 8 years (save for one README edit).

Values we have in the application.yml fall into four categories:

1. Actual application configuration, which we can replace with Rails' built-in method
2. Things that should be an attribute on Position Position not hiring #259
3. A few site-wide strings, which could be moved into I18n
4. Things removed in Deconfigure messages #613