Rename chelonia/db to chelonia.db and lock chelonia domain

[taoeffect]

Problem

The chelonia domain has access to various important state. It should not be possible to register a new selector in it after it is loaded.

Solution

1. Lock the entire chelonia domain.
2. Since chelonia/db/* selectors are intended to be overwritable after Chelonia is loaded, rename them to be under the chelonia.db domain.

Consider also loading data like CHELONIA_STATE using chelonia.db instead of gi.db.