feat: Store image uploads as attachments in database (#1144)

* First pass

* Documentation

* Added optional documentId relationship

* name -> key

* cleanup: No need for separate documentId prop

server/models/Attachment.js

@@ -0,0 +1,53 @@
+// @flow
+import path from 'path';
+import { DataTypes, sequelize } from '../sequelize';
+
+const Attachment = sequelize.define(
+  'attachment',
+  {
+    id: {
+      type: DataTypes.UUID,
+      defaultValue: DataTypes.UUIDV4,
+      primaryKey: true,
+    },
+    key: {
+      type: DataTypes.STRING,
+      allowNull: false,
+    },
+    url: {
+      type: DataTypes.STRING,
+      allowNull: false,
+    },
+    contentType: {
+      type: DataTypes.STRING,
+      allowNull: false,
+    },
+    size: {
+      type: DataTypes.BIGINT,
+      allowNull: false,
+    },
+    acl: {
+      type: DataTypes.STRING,
+      allowNull: false,
+      defaultValue: 'public-read',
+      validate: {
+        isIn: [['private', 'public-read']],
+      },
+    },
+  },
+  {
+    getterMethods: {
+      name: function() {
+        return path.parse(this.key).base;
+      },
+    },
+  }
+);
+
+Attachment.associate = models => {
+  Attachment.belongsTo(models.Team);
+  Attachment.belongsTo(models.Document);
+  Attachment.belongsTo(models.User);
+};
+
+export default Attachment;