1) Correctly unmask cursor and dispatch delta patches on successful {re,un}do.
2) Don't prompt to save twice on exit via Exit {accelerator,menu item}.
3) Fix cursor artifacts by always resetting origin point on DC whilst unmasking cursor cells.
4) Fix {re,un}do {accelerator,{menu,toolbar} item} desynchronisation with actual canvas journal undo level.
5) Remove scattered remnants of initial implementation of unimplemented italic support.
6) Replace rendering transparent cursor w/ manual blending over wx.GraphicsContext() due to canvas bitmap masking & performance degradation.
assets/text/TODO: updated.
