Fix "New Action" is enabled when Collection is readonly
Fix "New Action" is enabled when Collection is readonly

- Add action is activated when the todo is a StandardTodo
- The QLineEdit enabled state match the Add Action enabled state.
- When a StandardTodo is selected we check if the parent is different of
  a ProjectTodo, in this case the collection checked is the collection
  selected in the combobox and not the collection of the todo selected.

kolab-groupware/zanshin,sandsmark/zanshin,sandsmark/zanshin,sandsmark/zanshin,kolab-groupware/zanshin,kolab-groupware/zanshin