Make 'monitored_conditions' optional

[fabaff]

Description:

• Do not call update() in constructor
• Make monitored_conditions optional
• Update ordering

Pull request in home-assistant.github.io with documentation (if applicable): home-assistant/home-assistant.io#3142

Example entry for configuration.yaml (if applicable):

sensor:
  - platform: sonarr
    api_key: !secret sonarr_api

Checklist:

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.github.io

If the code does not interact with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• Tests have been added to verify that the new code works.