Add new types to Transmission sensors

[fabaff]

Description:

• Add paused_torrents and total_torrents
• Add data object
• Remove GLOBAL
• Add def available()
• Introduce PlatformNotReady

Related issue (if applicable): fixes 53530 (partially)

Pull request in home-assistant.github.io with documentation (if applicable): home-assistant/home-assistant.io#5393

Example entry for configuration.yaml (if applicable):

sensor:
  - platform: transmission
    host: 127.0.0.1
    monitored_variables:
      - 'current_status'
      - 'download_speed'
      - 'upload_speed'
      - 'active_torrents'
      - 'paused_torrents'
      - 'total_torrents'

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass

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

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

[MartinHjelmare]

Looks good!