LP1839562 Ang Vandelay Match Set Replace Mode

LP1839562 Ang Vandelay Match Set Replace Mode

Recover "Replace Mode" functionality in the Vandelay Match Set editor
interface, so existing nodes (e.g. And) may be replaced with other nodes
(e.g. Or) without modifying the rest of the tree structure.

Values (Record Attrs / MARC Fields) can replace other values.  Booleans
can replace any type of tree node.

Signed-off-by: Bill Erickson <berickxx@gmail.com>
Signed-off-by: Mary Llewellyn <mllewell@biblio.org>
Signed-off-by: Christine Morgan <cmorgan@noblenet.org>
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>