Onboarding modal (#1883)

* Basic onboarding modal that's shown to users once

* Lay out pages 2 through 5, add images, style modals (#1509)

* Lay out pages 2 through 5

Added images and laid out pages 2 through 5 in the jsx file. SCSS will
come, still working on just seeing if this works at all.

* Fix jsx errors, add images to modal pages, style modal pages

* Add animations to onboarding pager changes, improve wording and styling

* Finishing touches on the onboarding

* Add missing propTypes

* Update wording

app/controllers/home_controller.rb

@@ -7,6 +7,7 @@ class HomeController < ApplicationController
     @body_classes           = 'app-body'
     @token                  = find_or_create_access_token.token
     @web_settings           = Web::Setting.find_by(user: current_user)&.data || {}
+    @admin                  = Account.find_local(Setting.site_contact_username)
     @streaming_api_base_url = Rails.configuration.x.streaming_api_base_url
   end