libdocument: Add remove_annotation to DocumentAnnotations.

https://bugzilla.gnome.org/show_bug.cgi?id=649044
libdocument: add ev_mapping_list_remove

Needed to remove annotations from a mapping list

https://bugzilla.gnome.org/show_bug.cgi?id=649044
pdf: Implement remove_annotation virtual func

https://bugzilla.gnome.org/show_bug.cgi?id=649044
libview: add ev_view_remove_annotation

Hide annotation windows if necessary and unset selected
element before removing an annotation.

https://bugzilla.gnome.org/show_bug.cgi?id=649044
Add an option to remove annotations to the view popup menu

https://bugzilla.gnome.org/show_bug.cgi?id=649044