Pinned documents (#608)

* Migrations and API for pinned documents

* Documentation

* Add pin icon

* Fin.

* v0.2.0

* Remove pin from DocumentPreview, add general menu
Add Pinned documents header

* Tidy

* Fixed: Drafts appearing on collection home

server/migrations/20180225203847-document-pinning.js

@@ -0,0 +1,13 @@
+'use strict';
+
+module.exports = {
+  up: async (queryInterface, Sequelize) => {
+    await queryInterface.addColumn('documents', 'pinnedById', {
+      type: Sequelize.UUID,
+    });
+  },
+
+  down: async (queryInterface, Sequelize) => {
+    await queryInterface.removeColumn('documents', 'pinnedById');
+  }
+};