spectral: init at 2018-09-24

* needs at least qtgraphicaleffects not mentioned in docs
* doesn't want to use our libqmatrixclient, so let it use bundled
* took a few runs (or perhaps just patience with one) to populate,
  when my profile icon appeared it seemed ready-- then click it
  to see list of rooms and such.

pkgs/top-level/all-packages.nix

@@ -16989,6 +16989,8 @@ with pkgs;
 
   spectrwm = callPackage ../applications/window-managers/spectrwm { };
 
+  spectral = qt5.callPackage ../applications/networking/instant-messengers/spectral { };
+
   super-productivity = callPackage ../applications/networking/super-productivity { };
 
   wlc = callPackage ../development/libraries/wlc { };