This change introdoces a classification of commands by order in the undo stack. Undoing the last action will resend the
message of the last active token change and all messages changing the ui after that.
This change introduces the TaskScheduler, which queues and processes Tasks on a separate thread. The Task class provides
a common interface for deriving all specific tasks. A task can split it's processing into multiple update calls. The
TaskScheduler will update a task until it is finished or interrupt it when necessary. TaskGroups can be used to bundle
multiple Tasks together. So far only TaskGroupSequential was implemented which runs the Tasks in the set order.
TaskParseCxx utilizes the CxxParser to parse each source file in a single update call. Parsing can be interrupted using
the ESC key. The Statusbar shows the parsing progress.
Eberhard Graether