Cut down on boilerplate by using the (no longer that) new helper
macros. We don't care about breaking ABI in private libraries, so
use G_DECLARE_FINAL_TYPE even where the class struct used to be
exposed in the header, except for types we inherit from ourselves
(obviously) or where the class exposes any vfuncs (where changes
could affect inheritance in extensions).
* Add a keyring prompter based on GcrSystemPrompter
* Adds dependency on gcr version 3.3.5 or higher
* Not yet using unmerged support for non-pageable memory
https://bugzilla.gnome.org/show_bug.cgi?id=652459