Change preferences page into appearance, notifications, and other (#10977)

app/controllers/settings/notifications_controller.rb

...controllers/settings/preferences/appearance_controller.rb

...trollers/settings/preferences/notifications_controller.rb

app/controllers/settings/preferences_controller.rb

app/javascript/styles/mastodon/accounts.scss

app/javascript/styles/mastodon/forms.scss

app/views/layouts/mailer.html.haml

app/views/settings/preferences/appearance/show.html.haml

app/views/settings/preferences/notifications/show.html.haml

app/views/settings/preferences/show.html.haml

app/views/settings/profiles/show.html.haml

config/i18n-tasks.yml

config/initializers/simple_form.rb

config/locales/ar.yml

config/locales/ast.yml

config/locales/ca.yml

config/locales/co.yml

config/locales/cs.yml

config/locales/cy.yml

config/locales/da.yml