Column Header Tooltip - Prefix the Tooltip with the GroupColumn lineage

When a column's Header Tooltip is no not set, the grid displays the Header value which is not of much use.  If the Column is contained by one or more Group columns, the default Header Tooltip should display the the Column's Group column(s) lineage in addition to its Column Header:

Column HeaderTooltip = "<_GroupTop_._Header_>**:** _[_<_GroupChild_._Header_>**:**_]+_<_Column_._Header_>"