org.gnome.Geary.yaml: Add Pulse Audio and FDO sound theme

Former fixes Sent Mail plugin from being able to play, latter provides
it with something to play.

Fixes #752

org.gnome.Geary.json

@@ -15,6 +15,7 @@
         "--socket=x11",
         "--socket=wayland",
         "--device=dri",
+        "--socket=pulseaudio",
         "--share=network",
         "--talk-name=org.freedesktop.secrets",
         "--talk-name=org.gnome.Contacts",
@@ -215,6 +216,16 @@
                 }
             ]
         },
+        {
+            "name": "sound-theme-freedesktop",
+            "sources": [
+                {
+                    "type": "archive",
+                    "url": "http://people.freedesktop.org/~mccann/dist/sound-theme-freedesktop-0.8.tar.bz2",
+                    "sha256": "cb518b20eef05ec2e82dda1fa89a292c1760dc023aba91b8aa69bafac85e8a14"
+                }
+            ]
+        },
         {
             "name": "geary",
             "buildsystem": "meson",