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/Backlinks.js

@@ -0,0 +1,46 @@
+// @flow
+import * as React from 'react';
+import { observer } from 'mobx-react';
+import Fade from 'components/Fade';
+import Subheading from 'components/Subheading';
+import DocumentsStore from 'stores/DocumentsStore';
+import Document from 'models/Document';
+import Backlink from './Backlink';
+
+type Props = {
+  document: Document,
+  documents: DocumentsStore,
+};
+
+@observer
+class Backlinks extends React.Component<Props> {
+  componentDidMount() {
+    this.props.documents.fetchBacklinks(this.props.document.id);
+  }
+
+  render() {
+    const { documents, document } = this.props;
+    const backlinks = documents.getBacklinedDocuments(document.id);
+    const showBacklinks = !!backlinks.length;
+
+    return (
+      showBacklinks && (
+        <Fade>
+          <Subheading>Referenced By</Subheading>
+          {backlinks.map(backlinkedDocument => (
+            <Backlink
+              anchor={document.urlId}
+              key={backlinkedDocument.id}
+              document={backlinkedDocument}
+              showCollection={
+                backlinkedDocument.collectionId !== document.collectionId
+              }
+            />
+          ))}
+        </Fade>
+      )
+    );
+  }
+}
+
+export default Backlinks;