Provide privateui through a JSP page - fixes #455

This allows to control the access to `privateui/`.

Note 1: we replaced `privateui/index.html` to simply `privateui/`.
Note 2: update of Spring version from 2.5.6 to 3.2.5
Note 3: use of a configuration parameter (https://github.com/georchestra/georchestra/blob/issue455/config/defaults/ldapadmin/maven.filter#L6) to provide the public URI of this module. In JSP pages, the CSS files, for example, are changed from

```
	<link href='../account/css/bootstrap.min.css' rel="stylesheet" />
```

to

```
	<link href='${publicContextPath}/account/css/bootstrap.min.css' rel="stylesheet" />
```

ie. to

```
	<link href='/ldapadmin/account/css/bootstrap.min.css' rel="stylesheet" />
```

This way, the JSP files may be called for any URI depth level.

Note that we used an interceptor to add an attribute coming from the geOrchestra configuration,
the `/ldapadmin` publicContextPath. We could not use the common `${pageContext.request.requestURL}`
attribute in JSP files since it's equal to `/ldapadmin-private` (name of the webapp) in
the default geOrchestra installation.