Bug 7045: Use <<tag>> for default value placeholders

Bug 7045: Use <<tag>> for default value placeholders

When adding a biblio, the default value of a MARC subfield defined in
the frameworks can be used as placeholders to set the current date or
the surname of the logged in user (use cases?).
The different placeholders are 'YYYY', 'MM', 'DD', 'user'.
When adding an item, same behavior except that 'user' is not replaced.

This patch makes behaviors consistent between the 2 editors and
surrounds placeholders with << >>
We will now have: <<YYYY>>, <<MM>>, <<DD>> and <<USER>>

Test plan:
Define default values for biblio and item subfields.
Create a bibliographic record and attach it an item.
The default values should be used and replaced if you used placeholders.

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Katrin Fischer  <katrin.fischer@bsz-bw.de>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>