assets: fix deepcopy of webassets.filter.options
assets: fix deepcopy of webassets.filter.options

* FIX Implements `__deepcopy__` method for `webassets.filter.option` in
  order to fix unexpected behavior of the `option` class contructor.
  (addresses #2777) (fixes #2864) (closes #2921)

Reviewed-by: Javier Martin <ea6b80e26c65acc242d8916fb6eefa01b123cb69@cern.ch>
Signed-off-by: Jiri Kuncar <2bdffcb416fed3002465740d19a053a39918cbe5@cern.ch>

inveniosoftware/invenio,tiborsimko/invenio,tiborsimko/invenio,inveniosoftware/invenio