[INTERNAL] webpack: Use babel for polyfills / transpiling

- Use babel with preset-env and custom browser target list according to
browsers supported by UI5
- Remove polyfills

See: #112
Closes: #116

lib/client/browser.js

@@ -1,4 +1,3 @@
-require("url-polyfill");
 const istanbulLibCoverage = require("istanbul-lib-coverage");
 require("./discovery.js");
 

lib/client/discovery.js

@@ -1,5 +1,3 @@
-const Promise = require("es6-promise").Promise;
-const assign = require("lodash.assign");
 
 (function(window) {
 	const karma = window.__karma__;
@@ -23,7 +21,7 @@ const assign = require("lodash.assign");
 		if ( /^(\/test-resources\/(test-)?resources)/.test(sTestPage) ) {
 			sTestPage = sTestPage.slice("/test-resources".length);
 		}
-		this.aPages.push(assign({fullpage: sTestPage}, oConfig));
+		this.aPages.push(Object.assign({fullpage: sTestPage}, oConfig));
 	};
 
 	function getFile(sUrl) {
@@ -77,7 +75,7 @@ const assign = require("lodash.assign");
 									return !test.suite;
 								}).length === aTests.length;
 
-								resolve(assign({
+								resolve(Object.assign({
 									tests: aTests,
 									simple: bPass
 								}, oTestPageConfig));
@@ -87,7 +85,7 @@ const assign = require("lodash.assign");
 								if (frame.parentNode) {
 									frame.parentNode.removeChild(frame);
 								}
-								reject(assign({error: oError}, oTestPageConfig));
+								reject(Object.assign({error: oError}, oTestPageConfig));
 							});
 						};