Heal State saving changes & Neighbour save changes

Only save heal state to XML when its either done or failed.
Updated neighbor list is serialized only when manually refreshed and has
changes. Otherwise a completed Heal will save anyway.
Improve Node Deletion & Add "IsFailedNode" logic

Ensure a non-dead node cannot be deleted (controller does not allow it)
Add the IsFailedNode deletion. Once a node is deleted use an event to
remove the item from UI