housekeeping: upgrade to babel@7 (via #5450)

* Babel 7

* preserve module output; straighten out ES/CJS syntax

* add webpack TODOs

* remove unused Babel modules

* Update index.js

* install @babel/register

src/core/index.js

@@ -1,11 +1,15 @@
-import deepExtend from "deep-extend"
+// This file uses CommonJS require/exports syntax in order to export the SwaggerUI
+// function directly, instead of `{ default: fn SwaggerUI }`, which Babel would
+// generate if we used ESM syntax.
 
-import System from "core/system"
-import win from "core/window"
-import ApisPreset from "core/presets/apis"
+const deepExtend = require("deep-extend")
+
+const System = require("core/system").default
+const ApisPreset = require("core/presets/apis").default
+const AllPlugins = require("core/plugins/all").default
+const { parseSearch } = require("core/utils")
+const win = require("core/window")
 
-import * as AllPlugins from "core/plugins/all"
-import { parseSearch } from "core/utils"
 
 if (process.env.NODE_ENV !== "production" && typeof window !== "undefined") {
   win.Perf = require("react-dom/lib/ReactPerf")

src/core/plugins/all.js

@@ -2,6 +2,8 @@ import { pascalCaseFilename } from "core/utils"
 
 const request = require.context(".", true, /\.jsx?$/)
 
+const allPlugins = {}
+
 request.keys().forEach( function( key ){
   if( key === "./index.js" ) {
     return
@@ -13,5 +15,7 @@ request.keys().forEach( function( key ){
   // }
 
   let mod = request(key)
-  module.exports[pascalCaseFilename(key)] = mod.default ? mod.default : mod
+  allPlugins[pascalCaseFilename(key)] = mod.default ? mod.default : mod
 })
+
+export default allPlugins

src/core/plugins/oas3/wrap-components/model.jsx

@@ -1,7 +1,7 @@
 import React, { Component } from "react"
 import PropTypes from "prop-types"
 import { OAS3ComponentWrapFactory } from "../helpers"
-import { Model } from "core/components/model"
+import Model from "core/components/model"
 
 class ModelComponent extends Component {
   static propTypes = {

src/core/plugins/swagger-js/index.js

@@ -1,7 +1,7 @@
 import Swagger from "swagger-client"
 import * as configsWrapActions from "./configs-wrap-actions"
 
-module.exports = function({ configs, getConfigs }) {
+export default function({ configs, getConfigs }) {
   return {
     fn: {
       fetch: Swagger.makeHttp(configs.preFetch, configs.postFetch),