Restructure pkg/unittest and pkg/webdriver to follow the pub conventions.

tests/html/domparser_test.dart

-#library('DOMParserTest');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
+library DOMParserTest;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
 
 main() {
 
   useHtmlConfiguration();
 
   var isDOMParser = predicate((x) => x is DOMParser, 'is a DOMParser');
 
   test('constructorTest', () {
       var ctx = new DOMParser();
       expect(ctx, isNotNull);
       expect(ctx, isDOMParser);
   });
 }