display shortcuts conflicts directly in the dialog.

shortcuteditdialog take 2 new optionnal arguments:
- conflictCallback: a function or methode that return a shortcut
conflict name.
- cbArgs: the optional arguments to pass to conflictCallback
add a _num attribute
comment lines that remove the Shift modifier
add "setShortcuts" method
replace "editAction" by "findShortcutConflict" and "removeShortcuts"
update the edit dialog to remove the shortcuts conflicts
add the findShortcutConflict method