Convert backend code to ES modules

Bundling code now with Rollup for its flat bundling and tree shaking
support. Front end code still goes through Webpack for browser support.

lib/sandbox.js

@@ -18,15 +18,15 @@
  */
 "use strict";
 
-const vm = require("vm");
+import vm from "vm";
 
-const seedrandom = require("seedrandom");
+import seedrandom from "seedrandom";
 
-const common = require("./common");
-const device = require("./device");
-const extensions = require("./extensions");
-const logger = require("./logger");
-const scheduling = require("./scheduling");
+import * as common from "./common";
+import * as device from "./device";
+import * as extensions from "./extensions";
+import * as logger from "./logger";
+import * as scheduling from "./scheduling";
 
 // Used for throwing to exit user script and commit
 const COMMIT = Symbol();
@@ -327,7 +327,7 @@ function errorToFault(err) {
   return fault;
 }
 
-function run(
+export function run(
   script,
   globals,
   sessionContext,
@@ -416,5 +416,3 @@ function run(
     }
   }
 }
-
-exports.run = run;