feat #994 MultiAutoComplete: Highlighted mode interaction

This pull request allows users the following items:
1) When the user left-clicks on an item (that is not already highlighted), it becomes highlighted (if any other was already highlighted, it becomes de-highlighted)
2) When the user left-clicks on an already highlighted item, the latter goes into edit-mode.
3)  When an item is highlighted, pressing the backspace key removes the item and the previous one becomes highlighted. If there is no previous one, the following one becomes highlighted
4) When an item is highlighted, pressing the delete key removes the item and the following one becomes highlighted