1) With previous code each Annot object was reconstructed from the pdf object when
writing to PS, leading to the fact that writeDocSetup couldn't see the
generated appearance.
This patch makes writeDocSetup use the same Annots object returned by
Page::getAnnots.

2) This patch also enables each Annot subtype to control the exported
resources. AnnotFreeText uses this new method to export font information.

3) Comment fixed in Page.h: Page::getAnnots does *not* give away ownership, in
fact the returned object is destroyed by ~Page.