Migrate to font-awesome 5.0. (#8799)

app/helpers/application_helper.rb

...on/components/__tests__/__snapshots__/avatar-test.js.snap

app/javascript/mastodon/components/attachment_list.js

app/javascript/mastodon/components/bot_icon.js

app/javascript/mastodon/components/column_back_button.js

...javascript/mastodon/components/column_back_button_slim.js

app/javascript/mastodon/components/column_header.js

app/javascript/mastodon/components/icon_button.js

app/javascript/mastodon/components/load_gap.js

app/javascript/mastodon/components/status.js

...javascript/mastodon/features/account/components/header.js

...stodon/features/account_timeline/components/moved_note.js

...ript/mastodon/features/compose/components/compose_form.js

.../mastodon/features/compose/components/privacy_dropdown.js

...javascript/mastodon/features/compose/components/search.js

...pt/mastodon/features/compose/components/search_results.js

...javascript/mastodon/features/compose/components/upload.js

...t/mastodon/features/compose/components/upload_progress.js

app/javascript/mastodon/features/compose/index.js

app/javascript/mastodon/features/getting_started/index.js