* Added overview and integration page.
The overview outlines general concepts in Home Assistant such as what an integration is.
The Integration page contains steps that was at the end of the onboarding page. More detailed break to add an integration needs to be added.
* Added new images for device list and add-ons.
* Replaced device list with home assistant device page.
* Replaced overview with concepts and terminology.
Added screenshots to the page.
* Added images to adding Google Cast.
* Updated integrations with Google Cast as an example.
* Refined some of wording.
* Fixed Google Cast punctuation.
* Added scripts and scenes.
Replaced steps with action which is the same word used in other pages like /integrations/script/
* Removed concepts and terminology page because it has been submitted as a separate PR.
Updated navigation to match.
* Missed removing concepts and terminology in getting started index.
* Post merge changes:
* Moved integration details from onboarding to it's own page.
* Added integration page in getting started after concepts & terminology.
* Added tooltips to integration page.
* Change links to devices & services to Microsoft style.
* Additional changes from feedback.
