BibEdit: volatile values in record templates

• When creating a new record from a template, this record may now contain volatile subfield values, which serve as suggestions to the inputter, and are not real values. For example to indicate where the title should go, the template file should have: <subfield code="a">VOLATILE:Here is the title</subfield> The inputter will see 'Here is the title' in grey and the value will disappear when cataloger starts to edit it. (closes: #10260)