Redesign landing page (#10232)

app/controllers/about_controller.rb

app/controllers/public_timelines_controller.rb

app/controllers/tags_controller.rb

app/helpers/home_helper.rb

app/javascript/mastodon/containers/timeline_container.js

.../mastodon/features/standalone/community_timeline/index.js

...pt/mastodon/features/standalone/hashtag_timeline/index.js

...ipt/mastodon/features/standalone/public_timeline/index.js

...pt/mastodon/features/status/components/detailed_status.js

app/javascript/styles/mastodon/about.scss

app/javascript/styles/mastodon/forms.scss

app/javascript/styles/mastodon/widgets.scss

app/presenters/instance_presenter.rb

app/views/about/_features.html.haml

app/views/about/_forms.html.haml

app/views/about/_links.html.haml

app/views/about/_login.html.haml

app/views/about/_registration.html.haml

app/views/about/show.html.haml

app/views/layouts/public.html.haml