Bug fixes

Over the past few days I've worked on fixing some bugs found during testing (some that we had in the previous versions and some new):
- Undo needed to be pressed twice to work
- Undo after cut didn't show the sketch shapes that were used for cut
- After trying to redo when there were no more redo steps, the application sometimes crashed
- Cut to depth with negative values didn't work
- Cut through all for solids resulted in wrong shapes
- Pressing Cancel in the Chamfer window when the chamfer operation wasn't possible caused the selected shape to disappear

The bug I'm working on now causes some letters to disappear from the hinter text: