Refactor of documentation method for components (2019-0016)

[frenck]

Description:

Currently, we have tons of platform pages, that tells the user to go look at the component/hub page.
As a result of this, we have a lot of "Hub" pages, for things that are actually not a hub.

This PR tries to solve that and adds/optimizes some other things in the process.

Changes

• Adds support for specifying multiple categories in the ha_category frontmatter variable. While maintaining backwards compatibility.
• Ensured component still shows up in multiple categories (including search)
• Changed featured items category to ensure the component is only listed once (for the first category)
• Adds support for the ha_config_flow frontmatter variable, which will show a notice about this component being configurable via the UI on the component page.
• Adds a little more spacing around the logo's shown on the components page.
• Removes the list of other components in the same category from the component page (this reduces built times significantly): Added list of categories this component is in instead.
• Migrated the Ikea Tradfri as an example:
  • Removed platform pages (sensor, light, switch)
  • Added redirect_from to the main component page in order to keep old URL's working
  • Added Light, Switch and Sensor as categories, removed it from Hub.
  • Marked ha_config_flow since it does support that.

Pull request in home-assistant (if applicable): n/a

Checklist:

• Branch: next is for changes and new documentation that will go public with the next home-assistant release. Fixes, changes and adjustments for the current release should be created against current.
• The documentation follows the standards.

[balloob]

Awesome!

[klaasnicolaas]

This is great! 😄

[balloob]

@klaasnicolaas you can merge this one 👍

[klaasnicolaas]

Thnx for your PR @frenck 😄

[frenck]

Congratz on merging your first PR on the org @klaasnicolaas 🏅