Scrollable tables in settings pages (#4857)

app/javascript/styles/admin.scss

app/javascript/styles/tables.scss

app/views/admin/accounts/_card.html.haml

app/views/admin/accounts/index.html.haml

app/views/admin/accounts/show.html.haml

app/views/admin/domain_blocks/index.html.haml

app/views/admin/instances/index.html.haml

app/views/admin/reports/index.html.haml

app/views/admin/subscriptions/index.html.haml

app/views/auth/registrations/_sessions.html.haml

app/views/oauth/authorized_applications/index.html.haml

app/views/settings/applications/index.html.haml

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

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

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