Re-apply isort (#3908)

* Uncomment `default_section`

This now generates the correct warnings from isort

* isort sickrage

* isort sickbeard.providers

* isort sickbeard.clients

* isort sickbeard.databases

* isort sickbeard.indexers

* isort sickbeard.metadata

* isort sickbeard.name_parser

* isort sickbeard.notifiers

* isort sickbeard

* Enable import sorting for __init__.py files

* isort all sickbeard/**/__init__.py files

* isort sickbeard/__init_.py

and skip it until we don't have to import pytz before sickbeard/subtitles.py

* isort all sickrage/__init__.py files

* Sort __all__'s in sickbeard.providers and sickbeard.metadata