Doc: use standard wording in \brief commands

QDoc does some magic with the \class and \namespaces
and \brief commands, so the following wording must be used:
"The xxx class yyy ..."

Change-Id: Id231f30e8464898b776888d5423523de404aae34
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/projectexplorer/session.cpp

@@ -67,7 +67,7 @@ using namespace ProjectExplorer::Internal;
 /*!
      \class ProjectExplorer::SessionManager
 
-     \brief Session management.
+     \brief The SessionManager class manages sessions.
 
      TODO the interface of this class is not really great.
      The implementation suffers that all the functions from the