ui: manage logger instances and event filtering by core ui The setup code in blackbox needs more tweaks since it has lots of black magics. I'll fix them by follow-up patches. To be clear, the goal of this series is to provide a proper way for command server to install its own logger. I need it to debug in-memory repository cache.

extensions: add "uipopulate" hook, called per instance, not per process In short, this is the "reposetup" function for ui. It allows us to modify ui attributes without extending ui.__class__. Before, the only way to do that was to abuse the config dictionary, which is copied across ui instances. See the next patch for usage example.