DynamicColumnEditor improvements:
 - when hierarchy updates, finds and selects active column if not
previously found.
 - respects user category navigation when hierarchy updates after active
column was found.
 - selects active column when active parent category is clicked again.
Attribute selector now clears title when tool is disposed and unlinks
when the panel is closed.
CustomTree.scrollToAndSelectMatchingItem() now accepts an item parameter
and makes sure equivalent items not appearing in list do not get
deselected by Flex ListBase.

Change-Id: If5fe3df778d16fc033fa89267fc906c3a6bcc63f