mail-client/geary: various package fixes and touchups

mail-client/geary: various package fixes and touchups

* Fix tests (one needs virtx)
* Fix some minimum deps and sort in meson.build occurrence order
* Require webkit-gtk-2.26 to ensure a build conditional
  compatibility branch is used (building against 2.24 and then
  upgrading webkitgtk to 2.26 without geary rebuild may end up
  taking lots of CPU for some operations, afaiu)
* Fix automagic dep on ytnef (previously may have linked against
  it even with USE=-ytnef if the library was present)
* Drop conditional unwind support, as it's automagic and as it's
  a small dep, didn't fix it fully (much more involved than for
  ytnef)
* Move introspection,vala USE flag requirements to build-time
  only - these aren't needed at runtime for geary.
* Add missing itstool build depend
* Drop old LINGUAS based translation file dropping - it's not
  done for almost all meson based packages, and we aren't special
  in any way
* Drop dconf dep - again, don't think geary is more special than
  any other GSettings using application that don't dep on it for
  persistent configuration storage
* Explicit meson_options settings where appropriate, resorted in
  meson_options.txt order

Package-Manager: Portage-2.3.79, Repoman-2.3.12
Signed-off-by: Mart Raudsepp <leio@gentoo.org>