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

server/models/index.js

@@ -1,6 +1,7 @@
 // @flow
 import ApiKey from './ApiKey';
 import Authentication from './Authentication';
+import Backlink from './Backlink';
 import Collection from './Collection';
 import CollectionUser from './CollectionUser';
 import Document from './Document';
@@ -18,6 +19,7 @@ import View from './View';
 const models = {
   ApiKey,
   Authentication,
+  Backlink,
   Collection,
   CollectionUser,
   Document,
@@ -43,6 +45,7 @@ Object.keys(models).forEach(modelName => {
 export {
   ApiKey,
   Authentication,
+  Backlink,
   Collection,
   CollectionUser,
   Document,