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/models/Document.js

@@ -85,20 +85,6 @@ const Document = sequelize.define(
     revisionCount: { type: DataTypes.INTEGER, defaultValue: 0 },
     publishedAt: DataTypes.DATE,
     parentDocumentId: DataTypes.UUID,
-    createdById: {
-      type: DataTypes.UUID,
-      allowNull: false,
-      references: {
-        model: 'users',
-      },
-    },
-    lastModifiedById: {
-      type: DataTypes.UUID,
-      allowNull: false,
-      references: {
-        model: 'users',
-      },
-    },
     collaboratorIds: DataTypes.ARRAY(DataTypes.UUID),
   },
   {
@@ -129,6 +115,10 @@ Document.associate = models => {
     as: 'updatedBy',
     foreignKey: 'lastModifiedById',
   });
+  Document.belongsTo(models.User, {
+    as: 'pinnedBy',
+    foreignKey: 'pinnedById',
+  });
   Document.hasMany(models.Revision, {
     as: 'revisions',
     onDelete: 'cascade',