LP#1720345: ensure egEditFmRecord's customFieldTemplates is optional

LP#1720345: ensure egEditFmRecord's customFieldTemplates is optional

This patch ensures that the custom-field-templates attribute of
the eg-edit-fm-record directive is strictly optional, fixing a
regression for instances of that directive that don't need that
attribute.

To test
-------
[1] Apply the patch.
[2] Verify that the Server Administration | Copy Tag Types and
    and Local Administration | Copy Tags admin interfaces
    allow you to create and edit values.
[3] Verify that the Serials Administration | Prediction
    Pattern Templates interface continues to work.

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>