[session] upgrade session closed error from Exception to SessionClosedError
Exception is far too wide and we already have a SessionClosedError anyway.
Closes #2897696
Latest changes
--------------
* table of `all latest changes`_
Links below is providing useful RQL query example.
.. _all latest changes: view?rql=Any+M%2CX+WHERE+X+modification_date+M+ORDERBY+M+DESC+LIMIT+30