Convert require statements to import statements

This is currently a non-working version of the App class because
the SEOAssessor and Presenter are objects instead of the correct
class. However, this commit eliminates all possibilities of require
statements in our base file being the culprit of the out of memory
errors.

lib/app.js

@@ -1,24 +1,27 @@
-const yoast = require('yoastseo');
+import {
+  ContentAssessor,
+  Paper,
+  Pluggable,
+  Researcher,
+  string,
+} from 'yoastseo';
 
-const defaultsDeep  = require( "lodash/defaultsDeep" );
-const isObject      = require( "lodash/isObject" );
-const isString      = require( "lodash/isString" );
-const isUndefined   = require( "lodash/isUndefined" );
-const isEmpty       = require( "lodash/isEmpty" );
-const forEach       = require( "lodash/forEach" );
+// TODO: Either depend on lodash or don't use this.
+import _ from 'lodash';
 
-const ContentAssessor = yoast.ContentAssessor;
-const Paper           = yoast.Paper;
-const Pluggable       = yoast.Pluggable;
-const Researcher      = yoast.Researcher;
-const SEOAssessor     = yoast.SEOAssessor;
+const defaultsDeep  = _.defaultsDeep;
+const isObject      = _.isObject;
+const isUndefined   = _.isUndefined;
 
 // Import the following 'private' classes
-const CornerstoneSEOAssessor      = require( "yoastseo/js/cornerstone/seoAssessor.js" );
-const CornerstoneContentAssessor  = require( "yoastseo/js/cornerstone/contentAssessor.js" );
-const AssessorPresenter           = require( "yoastseo/js/renderers/AssessorPresenter.js" );
+// TODO: This should probably be public: https://github.com/Yoast/YoastSEO.js/issues/1878
+// const SEOAssessor                 = require( "yoastseo/js/seoAssessor.js");
+const SEOAssessor = {};
+// TODO: We should replace this with our own presenter.
+// const AssessorPresenter           = require( "yoastseo/js/renderers/AssessorPresenter.js" );
+const AssessorPresenter = {};
 
-const removeHtmlBlocks = require( "yoastseo/js/stringProcessing/htmlParser.js" );
+const removeHtmlBlocks = string.removeHtmlBlocks;
 
 /**
  * Default config for Real Time SEO
@@ -54,6 +57,7 @@ function verifyArguments( args ) {
 }
 
 // TODO: Add TitleWidth as required data for getData callback or implement calculator
+// there is a textWidth calculator in the YoastSEO library.
 
 /**
  * This should return an object with the given properties
@@ -197,7 +201,6 @@ App.prototype.initializeSEOAssessor = function( args ) {
   }
 
   this.defaultSeoAssessor = new SEOAssessor( this.i18n, { marker: this.config.marker } );
-  this.cornerStoneSeoAssessor = new CornerstoneSEOAssessor( this.i18n, { marker: this.config.marker } );
 
   // Set the assessor
   if ( isUndefined( args.seoAssessor ) ) {
@@ -219,7 +222,6 @@ App.prototype.initializeContentAssessor = function( args ) {
   }
 
   this.defaultContentAssessor = new ContentAssessor( this.i18n, { marker: this.config.marker, locale: this.config.locale }  );
-  this.cornerStoneContentAssessor = new CornerstoneContentAssessor( this.i18n, { marker: this.config.marker, locale: this.config.locale } );
 
   // Set the content assessor
   if ( isUndefined( args.contentAssessor ) ) {