`falsey` config values are not persisted

In an effort to keep our `application.rb` file as close to a default rails app as possible, we chose to configure console1984 in an initializer using a `Rails.application.reloader.to_prepare` block.

```
Rails.application.reloader.to_preparse do
Rails.application.configure do
config.console1984.incinerate = false
end
end
```

What we found out though is that the `falsey` values are not persisted. The current behavior of `set_from` is such that not present values are not assigned. I've opened a [PR](https://github.com/basecamp/console1984/pull/133) that aligns the behavior of console1984 with the behavior in audits1984.

Review the set_from behavior described in the issue and compare it with linked PR #133, which aligns console1984 with audits1984. Done means configuration values explicitly set to false are persisted when configured through the Rails reloader block.

Written by the indexing model from the issue text.