optional content defaults and page copies

[plaisted]

Optional content is copied with pages but the defaults for show / no show are not brought with since they are in the document catalog. There may be similar issues with acroforms although haven't looked at those at all.

Potential fix:

• keep ref to doc on pages
• check catalog on copy and add metadata to pages

Alternatively we could do it during parsing the page tree, and add metadata automatically but not sure how simple that is.