Add missing (nullable) annotations, assorted minor introspection fixes

https://bugzilla.gnome.org/show_bug.cgi?id=729987
introspection: Fix some g-ir-scanner warnings

https://bugzilla.gnome.org/show_bug.cgi?id=729987
Add missing array annotations for binary data

https://bugzilla.gnome.org/show_bug.cgi?id=729987