Redo/Undo System is broken

[giannissc]

Rnote does undo/redo does not work as expected. When I press Ctrl + Z i expect it to undo the last action however what it currently does is starts undoing sometimes from the beginning, sometimes it undoes the last few actions and them jumps to the beginnning. The behaviour is very erratic and not consistent every time. See videos below:

redo-undo.mp4

redo-undo-2.mp4

[giannissc]

The lines in the document indicate the order things were drawn

[flxzt]

I believe it should behave better now, at least not as random anymore.
However as I mentioned in #27, the undo / redo currently only works as trash / untrash strokes, it does not have memory for resizing, translating or any other stroke operations. I'll keep the issue open for tracking to implement this feature ( probably as more state and methods in the chrono component ).

[flxzt]

with #149 it should now be fixed and behave like in other apps ( including selection modifications, duplicating, trashing strokes, etc.) , but I'll keep this open for until after the release, for feedback.