Fix #100 - Add "back" button to certain views

app/assets/javascripts/components/actions/accounts.jsx

app/assets/javascripts/components/actions/timelines.jsx

.../javascripts/components/components/column_back_button.jsx

app/assets/javascripts/components/containers/mastodon.jsx

...scripts/components/features/account/components/header.jsx

app/assets/javascripts/components/features/account/index.jsx

app/assets/javascripts/components/features/status/index.jsx

app/assets/javascripts/components/reducers/timelines.jsx

app/controllers/api_controller.rb

app/models/feed.rb