Modify a bunch of stuff.

- Modify 'playback' & 'spotify' examples.
- Rename 'audiopia::async::service' => 'audiopia::eventloop'
  and 'audiopia::async::object_interface' => 'audiopia::event_object_interface'
- Add option to remember Spotify's login credential.
- Modify 'audiopia::spotify::client::wait' to handle multiple states.
- Modify 'audiopia' utility to support Spotify's relogin.
- Modify 'audiopia' utility to color current track in collection-view.
- Add a help message function to all aggregator initializers.
- Add support for modifiable options in aggregator initialization.
- Python aggregators use there docstrings as help message.
- Fix typo.
Add support for searching within results (live).
Add support for querying from db with cli arg.

If the 1st argument is not a valid directory path and not a registered aggregator,
we use the argument as a search term to query the DB with.
__aggregator_initializer takes a 2nd help argument.
Add support for global search queries.

A global search query uses all registered aggregators as a global aggregator.
To support the global search, an aggregator must:

1) initialize with no parameters.
2) uses the '--filter' option and use it as global search.
Restrict search to alphanumeric characters.