rewrote OnboardingPage:
* decomposed into separate widgets
* now content stays centered on wide screens (set so width won't expand further than 480px)
* pageController is now properly disposed
* added some more code changes to
* main (error widget builder)
* brand_header (centerTitle instead of empty actions list)
* console_page (listener callback fix, used gaps instead of SizedBox'es, added keys to list items)
* service_page (just cleaner build method)
* removed some dead code
Co-authored-by: Aliaksei Tratseuski <aliaksei.tratseuski@gmail.com>
Reviewed-on: https://git.selfprivacy.org/SelfPrivacy/selfprivacy.org.app/pulls/444
Co-authored-by: aliaksei tratseuski <misterfourtytwo@noreply.git.selfprivacy.org>
Co-committed-by: aliaksei tratseuski <misterfourtytwo@noreply.git.selfprivacy.org>