feat: Backlinks (#979)

* feat: backlinks

* feat: add backlinkDocumentId to documents.list

* chore: refactor
fix: create and delete backlink handling

* fix: guard against self links

* feat: basic frontend
fix: race condition

* styling

* test: fix parse ids

* self review

* linting

* feat: Improved link styling

* fix: Increase clickable area at bottom of doc / between references

* perf: global styles are SLOW

app/scenes/Document/components/Backlink.js

@@ -0,0 +1,68 @@
+// @flow
+import * as React from 'react';
+import { observer } from 'mobx-react';
+import { Link } from 'react-router-dom';
+import styled from 'styled-components';
+import PublishingInfo from 'components/PublishingInfo';
+import Document from 'models/Document';
+
+type Props = {
+  document: Document,
+  anchor: string,
+  showCollection?: boolean,
+  ref?: *,
+};
+
+const DocumentLink = styled(Link)`
+  display: block;
+  margin: 0 -8px;
+  padding: 6px 8px;
+  border-radius: 8px;
+  border: 2px solid transparent;
+  max-height: 50vh;
+  min-width: 100%;
+  overflow: hidden;
+  position: relative;
+
+  &:hover,
+  &:active,
+  &:focus {
+    background: ${props => props.theme.listItemHoverBackground};
+    outline: none;
+  }
+`;
+
+const Title = styled.h3`
+  max-width: 90%;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  font-size: 14px;
+  margin-top: 0;
+  margin-bottom: 0.25em;
+  white-space: nowrap;
+  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen,
+    Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
+`;
+
+@observer
+class Backlink extends React.Component<Props> {
+  render() {
+    const { document, showCollection, anchor, ...rest } = this.props;
+
+    return (
+      <DocumentLink
+        to={{
+          pathname: document.url,
+          hash: `d-${anchor}`,
+          state: { title: document.title },
+        }}
+        {...rest}
+      >
+        <Title>{document.title}</Title>
+        <PublishingInfo document={document} showCollection={showCollection} />
+      </DocumentLink>
+    );
+  }
+}
+
+export default Backlink;