Move date, time & retry utility code to `util/` dir

As per #648, move several modules containing utility functions which
have no dependencies on other code to `src/sidebar/util`.

src/sidebar/components/timestamp.js

 'use strict';
 
-var dateUtil = require('../date-util');
+var dateUtil = require('../util/date');
 
 // @ngInject
 function TimestampController($scope, time) {

src/sidebar/index.js

@@ -221,7 +221,7 @@ module.exports = angular.module('h', [
   .value('raven', require('./raven'))
   .value('serviceConfig', serviceConfig)
   .value('settings', settings)
-  .value('time', require('./time'))
+  .value('time', require('./util/time'))
   .value('urlEncodeFilter', require('./filter/url').encode)
 
   .config(configureCompile)

src/sidebar/services/api-routes.js

 'use strict';
 
-var { retryPromiseOperation } = require('../retry-util');
+var { retryPromiseOperation } = require('../util/retry');
 
 /**
  * A service which fetches and caches API route metadata.

src/sidebar/services/session.js

 'use strict';
 
 var events = require('../events');
-var retryUtil = require('../retry-util');
+var retryUtil = require('../util/retry');
 
 var CACHE_TTL = 5 * 60 * 1000; // 5 minutes
 

src/sidebar/test/retry-util-test.js → src/sidebar/util/test/retry-test.js

 'use strict';
 
-var retryUtil = require('../retry-util');
-var toResult = require('../../shared/test/promise-util').toResult;
+var retryUtil = require('../retry');
+var toResult = require('../../../shared/test/promise-util').toResult;
 
-describe('retry-util', function () {
+describe('sidebar.util.retry', function () {
   describe('.retryPromiseOperation', function () {
     it('should return the result of the operation function', function () {
       var operation = sinon.stub().returns(Promise.resolve(42));

src/sidebar/test/time-test.js → src/sidebar/util/test/time-test.js

@@ -38,7 +38,7 @@ var FIXTURES_NEXT_FUZZY_UPDATE = [
   [8 * year, null],
 ];
 
-describe('time', function () {
+describe('sidebar.util.time', function () {
   var sandbox;
 
   beforeEach(function () {