Add some UI for user-defined domain blocks (#6628)

* Keep list of blocked domains

Might be overkill, but I'm trying to follow the same logic as for blocked users

* Add basic domain block UI

* Add the domain blocks UI to Getting Started

* Fix undefined URL in `fetchDomainBlocks`

* Update all known users' domain_blocking relationship instead of just one's

app/javascript/mastodon/components/domain.js

@@ -0,0 +1,42 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+import IconButton from './icon_button';
+import { defineMessages, injectIntl } from 'react-intl';
+import ImmutablePureComponent from 'react-immutable-pure-component';
+
+const messages = defineMessages({
+  unblockDomain: { id: 'account.unblock_domain', defaultMessage: 'Unhide {domain}' },
+});
+
+@injectIntl
+export default class Account extends ImmutablePureComponent {
+
+  static propTypes = {
+    domain: PropTypes.string,
+    onUnblockDomain: PropTypes.func.isRequired,
+    intl: PropTypes.object.isRequired,
+  };
+
+  handleDomainUnblock = () => {
+    this.props.onUnblockDomain(this.props.domain);
+  }
+
+  render () {
+    const { domain, intl } = this.props;
+
+    return (
+      <div className='domain'>
+        <div className='domain__wrapper'>
+          <span className='domain__domain-name'>
+            <strong>{domain}</strong>
+          </span>
+
+          <div className='domain__buttons'>
+            <IconButton active icon='unlock-alt' title={intl.formatMessage(messages.unblockDomain, { domain })} onClick={this.handleDomainUnblock} />
+          </div>
+        </div>
+      </div>
+    );
+  }
+
+}