Due to former duplicated code (between lambda connected to smartlist selection change
and the slot of smartlist clicked) and wrong signal caught from smartlist
(selectionChanged instead of currentChanged), the messagingPage was going blank
in certain cases.

Fixed by refactoring the code and catching the signal currentChanged with
smartlistCurrentChanged slot.

Change-Id: If6d2461fc203318708e9c373c8ccb8294207db37
Tuleap: #1314