Add new 'group' web tag, 'cssClass' attribute in some web tags and bug fixes in 'DragAndDrop'

## Summary
* Add a ```group``` tag for web tests.
* Error trace improvement in ```group``` tag.
* Add ```cssClass``` attribute in ```AssertCheckBox```, ```ClickCheckbox``` and ```AssertPresent```.
* Bug fix - ```DragAndDrop``` now does wait that javascript has finished (100ms).
* Bug fix - ```Editform``` xsd definition was linked to swing tags.


## Add a ```group``` tag for web tests
--------------------------------------

### Context
We need a ```group``` tag in web test to make the tests more easily readable.

### Description
A ```group``` tag has been added, like in gui-tests.

### Example

```xml
    <web-test session="1">
        <group name="FrenchLanguage">
            <group name="mainPage">
                <group name="assertTabbedPane" enable="true">
                    <assertLink target="production.html" present="false"/>
                    <assertText>Production</assertText>
                    <assertLink target="recette.html">Recette</assertLink>
                </group>
				.....
            </group>				
        </group>			
	</web-test>	
```

## Error trace improvement  in ```Group``` tag
--------------------------

### Context
When using ```Group``` tag in web and gui test, if an error occurs, it makes sense to display the hierarchy path.

### Description
Error messages have been improved to display the group hierachy in which the failure has happened.
Moreover, if it is a web test, the page content is now spooled before the error message.

### Example

Sample Error message:

```

C:\Users\marcona\AppData\Local\Temp\SwitchLanguage.xml:47: 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Spool page: https://localhost:35743/production.html
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

     -->PAGE CONTENT
	 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Erreur web-test '1' Step 1 du groupe 'FrenchLanguage > mainPage > assertLeftPanel' (AssertLink)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Le lien 'Habilitation IT' n'a pas la bonne cible.
Attendu : 'eeeehttps://ldapbv.intradit.net/adsbv-online/pages/AdsbvOnline.jsp'
Obtenu : 'https://ldapbv.intradit.net/adsbv-online/pages/AdsbvOnline.jsp'
...

```

## Add ```cssClass``` attribute in ```AssertCheckBox```, ```ClickCheckbox``` and ```AssertPresent```  
---------------------------------------------------------------------------------

### Context
Adding ```cssClass``` and ```index``` attributes in tags make the web-tests more readable.

### Description
```cssClass``` and ```index``` attribute have been added in AssertCheckBox ClickCheckbox and AssertPresent.

### Example

```xml
   <assertText containerCssClass="backToHomePage">Retour</assertText>
   <clickLink cssClass="backBouton" index="3"/>
...   
   <assertPage title="Mes messages"/>
   <assertPresent cssClass="inputClass"/>
```

## Bug fix - ```DragAndDrop``` now does wait that javascript has finished (100ms)
---------------------------------------------------------------------------

### Context
In ```DragAndDrop``` web step, we sometimes need to tell htmlunit to wait for javascript to be finished.

### Description
We tell htmlunit to wait for 100 ms for each drag and drop steps : ```mouseDown```, ```mouseMove``` and ```mouseUp```.
```Clic```, ```ClickLink``` and ```ClicButton``` have also been improved to wait for 100 ms that javascript has finished.

## Bug fix - ```Editform``` xsd definition was linked to swing tags 
-----------------------------------------------------------------------------------------------------------

### Context
In ```Editform```, ```AssertCheckBox``` and ```ClickCheckbox``` were declared in xsd, as if they were swing tags 

### Description
Xsd has been refactored and generified.