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

shared/utils/parseDocumentIds.js

@@ -0,0 +1,29 @@
+// @flow
+import MarkdownSerializer from 'slate-md-serializer';
+const Markdown = new MarkdownSerializer();
+
+export default function parseDocumentIds(text: string) {
+  const value = Markdown.deserialize(text);
+  let links = [];
+
+  function findLinks(node) {
+    if (node.type === 'link') {
+      const href = node.data.get('href');
+
+      if (href.startsWith('/doc')) {
+        const tokens = href.replace(/\/$/, '').split('/');
+        const lastToken = tokens[tokens.length - 1];
+        links.push(lastToken);
+      }
+    }
+
+    if (!node.nodes) {
+      return;
+    }
+
+    node.nodes.forEach(findLinks);
+  }
+
+  findLinks(value.document);
+  return links;
+}