ViewManager::sessionList() : order the list by tab order

This report is related to https://bugs.kde.org/show_bug.cgi?id=298775 and the ongoing efforts initiated by @carlosbalves in !266 (merged) (thanks, Carlos !)

As mentioned in ViewManager.h, the session list given by ViewManager::sessionList() is currently unsorted.

On the user side, further ordering from oldest to newest session is trivial, e.g. by doing

dbus-send --dest="${KONSOLE_DBUS_SERVICE}" --type=method_call --print-reply /Windows/1 org.kde.konsole.Window.sessionList |grep string |cut -d\" -f2|sort -n

But it is currently impossible to have a session list whose order is the same as for the tabs -- which might be different since the user might changed the tabs order

Therefore, it seems best to me that ViewManager::sessionList() orders its output according to the tabs order.

It would allow users to jump to their desired session much more easily.