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

tests/html/websql_test.dart

-#library('WebDBTest');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
+library WebDBTest;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
 
 void fail(message) {
   guardAsync(() {
       expect(false, isTrue, reason: message);
     });
 }
 
 Future<SQLTransaction> createTransaction(Database db) {
   final completer = new Completer<SQLTransaction>();
 
@@ skipping 92 matching lines @@
           expect(resultSet.rows.length, 1);
           var row = resultSet.rows.item(0);
           expect(row.containsKey(columnName), isTrue);
           expect(row[columnName], 'Some text data');
         });
       }))
       .chain(dropTable(tableName))
       .then(expectAsync1((tx) {}));
   });
 }