Fixes against causes of annotation data loss + Improved GUI message logic

1) If the user had previously annotated the document with an old okular
version and the document contains existing annotations and no /Encrypt
(ie the case where annotation changes are no longer saved locally), make
Document::saveDocumentInfo write the original unmodified local
annotations back to XML, so that it seems that the original file was not
changed. If the user makes annotation changes, code from previous
patches already asks him to save them to a different document on close.

2) Ask "Save changes?" if the user has modified annotations in a .okular
archive.


3) Turned a "sorry" message in a "information" (with dontshowthisagain),
because now we also have the "Save changes?" prompt to inform the user.

4) Suppressed all annotation-related message boxes on document opening