ListResponse changed to SessionIdsList, since it was only user for it.

The ListResponse was used for returning the list of sessionsIds stored by the protocolSessionManager. When it was serialized, the structure of the xml was something like:
```xml
<ListResponse >
   <list xs:namespace...... xsd:string> 1238123-123131-313 </list>
<ListResponse>
```
So the ListResponse was modified to return the following format:
 ```xml
<SessionsIds>
    <session>1212556-231231-123</list>
</SessionsIds>
```