instead, schedule a queued finished signal to unregister the listener after the handler has finished.
See PythonActivity.java in P4A for why this probably causes the most often occurring crash we see on the Play Store:
```
Exception java.lang.RuntimeException:
at android.app.ActivityThread.deliverResults (ActivityThread.java:5164)
at android.app.ActivityThread.handleSendResult (ActivityThread.java:5205)
at android.app.servertransaction.ActivityResultItem.execute (ActivityResultItem.java:51)
at android.app.servertransaction.TransactionExecutor.executeCallbacks (TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute (TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage (ActivityThread.java:2136)
at android.os.Handler.dispatchMessage (Handler.java:106)
at android.os.Looper.loop (Looper.java:236)
at android.app.ActivityThread.main (ActivityThread.java:8061)
at java.lang.reflect.Method.invoke
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:656)
at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:967)
Caused by java.util.ConcurrentModificationException:
at java.util.ArrayList$Itr.next (ArrayList.java:860)
at org.kivy.android.PythonActivity.onActivityResult (PythonActivity.java:218)
at android.app.Activity.dispatchActivityResult (Activity.java:8501)
at android.app.ActivityThread.deliverResults (ActivityThread.java:5157)
```
This reverts commit 21ffe32157.
This layout is difficult to get right. Both the old and the new layout are somewhat buggy.
Reverting this only on the 4.5.x release branch. We can improve it on master.
The old layout has been out there in releases for many months, so it is safer to just use
that in the release branch for now.
In fact, semantically it might be more correct to only trigger 'blockchain_updated' and not 'network_updated' here...
Anyway, 'blockchain_updated' should be triggered whenever the Blockchain object gets longer (or changes otherwise).
In particular, in qml, the NetworkOverview only updates the displayed height on 'blockchain_updated'.
