Add SingleValMenuCol

Add SingleValMenuCol as a child of MenuCol.  Does the same as the
SingleValCol - Column Pair:  only the first line of SingleValMenuCol can
be changed, all others have editting disabled.
Add SingleValMenuCol to TestDevices/TestMenu/

Add SingleValeMenuCol demo to the test device.
MenuCol changes push through disabled cells

While testing SingleValMenuCol, found that MenuCol (& children) were not
properly pushing values down the table through disabled cells.  Inserted a
call into MenuDo to fix this.