made notes of undoable actions
Merge branch 'master' of github.com:aurule/HiToDo into undo
Began adding undo and redo. Covered task add and notes change.
Added undo/redo for Title field.
Added undo/redo for assigner, assignee, and status.
Fixed handling of dates within treemodel.
Added undo/redo for Est, Spent, and Priority fields.
Added undo/redo for Done field.
Clear undo/redo buffers on file open or new file.
Improved cut/copy/paste functionality.
Improved paste behavior.
Fixed potential crash due to type mismatch in est and spent committers.
Added headers for paste and del undo/redo.
Elaborated undo comments.
Merge branch 'undo' of github.com:aurule/HiToDo into undo

Conflicts:
	HiToDo.py
Added undo/redo for paste operations.
Added undo/redo for task delete.