Allow only authenticated users

Defines a config parameter in gpt.xml that, if set to true, denies search to anonymous users (i.e. login is required). 
```
		<parameter key="AllowOnlyAuthenticatedUser" value="true"/>
```
With these modifications the Home page will not have the Search and Browse menus; this page should be substituted with a help or startup page. Direct access to Search and Browse is also controlled (catalog/main/search/search.page and catalog/main/search/browse/browse.page). Detail page as well as CSW endpoint are NOT controlled; a correct GetRecords request will be honoured: to avoid so some additional control (for example URL mapping rules)  must be implemented.