Make registration work

This uses a new compiled jar based on the current `headless-stdin`
branch:
* https://code.briarproject.org/briar/briar/tree/3f6e5fe098a45977458e9f717418692105b81c61
* https://media.dorfbrunnen.eu/briar/jars/002/briar-headless.jar

app.briar.gtk.json

@@ -57,8 +57,8 @@
             "sources": [
                 {
                     "type" : "file",
-                    "url" : "https://media.dorfbrunnen.eu/briar/patched/briar-headless.jar",
-                    "sha256": "a2b8f35cc55a3bf374d0f7666e852b556404146984893a0a694a457c296846be"
+                    "url" : "https://media.dorfbrunnen.eu/briar/jars/002/briar-headless.jar",
+                    "sha256": "039352ecde9abff63f954efe79402097f02720d9fd61e386e9bf168ce9110669"
                 }
             ]
         },