Vision2u Vision2

implement undo and redo for drop commands
Defect: VIS-59

implement undo and redo for resizing states
Defect: VIS-59

test and fix bugs in enabling/disabling Undo and Redo buttons.
Defect: VIS-59

complete undo and redo for editing parameters in state, command and variable panels
Defect: VIS-56

Fixed export help function; update Undo and Redo icons.
Defect: VIS-56

fix issues and drop down button for undo and redo
Defect: VIS-56

basic implementation for drop down button of undo and redo

early implementation of shortcuts for undo and redo
Defect: VIS-56

implement undo and redo for adding and deleting variables of Command. Add constant that specifieds max call stack.
Defect: VIS-56

implement commands for adding and deleting state variables.
Defect: VIS-56