Main Clair logic is changed in worker, updater, notifier for better adapting
ancestry schema. Extensions are updated with the new model and feature lister
and namespace detector drivers are able to specify the specific listers and
detectors used to process layer's content. InRange and GetFixedIn interfaces
are added to Version format for adapting ranged affected features and next
available fixed in in the future. Tests for worker, updater and extensions
are fixed.
This puts config in its relevant location and moves functions around
loading config files into the main package.
As a side effect of removing cyclic imports for the API config, the
context library is no longer used.
