Share Permissions (#761)

* Share restrictions

* Tweak language, add spec

server/migrations/20180819054252-disable-sharing.js

@@ -0,0 +1,12 @@
+module.exports = {
+  up: async (queryInterface, Sequelize) => {
+    await queryInterface.addColumn('teams', 'sharing', {
+      type: Sequelize.BOOLEAN,
+      allowNull: false,
+      defaultValue: true
+    });
+  },
+  down: async (queryInterface, Sequelize) => {
+    await queryInterface.removeColumn('teams', 'sharing');
+  }
+}