1627 - Ticket ref sometimes duplicate

This code is a drop in replacement based on  an abstract counter based on an abstract keyValue store.
The counter can be
 - class based (in this case the counter is initialized on max(id) + 1
 - key based (in this case the counter starts at 0)

Important: on both cases the counter is no more kept aligned with the primary key.

This lead to a MySQL8 compatible implementation.

datamodels/2.x/itop-tickets/datamodel.itop-tickets.xml

@@ -203,12 +203,10 @@
     public function DBInsertNoReload()
     {
           $oMutex = new iTopMutex('ticket_insert');
-          $oMutex->Lock();
-          $iNextId = MetaModel::GetNextKey(get_class($this));
+          $iNextId = ItopCounter::IncClass(get_class($this));
           $sRef = $this->MakeTicketRef($iNextId);
           $this->SetIfNull('ref', $sRef);
           $iKey = parent::DBInsertNoReload();
-          $oMutex->Unlock();
           return $iKey;
     }
         ]]></code>