feat: Permissions for board members

Closes #262

server/db/migrations/20220815155645_add_permissions_to_board_membership_table.js

@@ -0,0 +1,18 @@
+module.exports.up = async (knex) => {
+  await knex.schema.table('board_membership', (table) => {
+    /* Columns */
+
+    table.text('role').notNullable().defaultTo('editor');
+    table.boolean('can_comment');
+  });
+
+  return knex.schema.alterTable('board_membership', (table) => {
+    table.text('role').notNullable().alter();
+  });
+};
+
+module.exports.down = (knex) =>
+  knex.schema.table('board_membership', (table) => {
+    table.dropColumn('role');
+    table.dropColumn('can_comment');
+  });