Added comment
Added possibility to have undoTypes per instance

Instead of one global UndoTypes object, every UndoManager now has the
possibility to have a custom UndoTypes object. The great thing: Nothing
changes for those who don't want to use a custom one. Global changes of
the undoTypes still take effect on all instances, just as changes on
one instance don't intermingle with the global object.
Repositioned the definition of the "reset" UndoType
Minor changes or bugfixes
Added "addUndoType", "changeUndoType" and "removeUndoType" to manipulate the global and the local UndoTypes-Object