Add libkundo2 to Calligra

kundo2 is a fork of Qt's Undo Framework (QUndoStack, QUndoView, ...).
It contains two bugfixes the are going to be available only in Qt 4.8:
https://qt.gitorious.org/qt/qt/merge_requests/1212
https://qt.gitorious.org/qt/qt/merge_requests/2610

To start using kundo2, one should port Calligra to it. This can be done
by adding target_link_libraries(... kundo2) into CMakeLists.txt files
for all modules from Calligra that use Qt Undo Framework, and by
switching from QUndo**** classes to KUndo2**** classes.
(switching to KUndo2 classes can easily be done by using a script)

After Calligra starts requiring Qt 4.8+, this library can be removed,
because it has no advantages over Qt's Undo Framework 4.8.