ColumnResizer: Suppress focus outline on resizer node
CompoundColumns: Add logic to support ColumnHider and ColumnResizer

Note that this currently requires that ColumnHider and/or ColumnResizer be
mixed in *before* CompoundColumns, since CompoundColumns will extend
methods from the other two.  This is in contrast to ColumnSet, which needs
to be mixed in *after* CompoundColumns.

Also includes some general cleanup.
Fix a problem with combining ColumnSet, ColumnResizer and CompoundColumns.