Fix various memory leaks reported by LeakCanary

- In some places, we weren't nulling out references to destroyed objects. This
  fixes that.
- (These were all discovered via LeakCanary instrumentation, and the fixes are
  hopefully rather straightforward-looking.)

(cherry picked from commit 364502d1a3def0e8895c463b72c8f48e45508214)

src/main/java/eu/siacs/conversations/ui/ConversationFragment.java

@@ -1216,6 +1216,14 @@ public class ConversationFragment extends XmppFragment implements EditMessage.Ke
         }
         return binding.getRoot();
     }
+    @Override
+    public void onDestroyView() {
+        super.onDestroyView();
+        Log.d(Config.LOGTAG,"ConversationFragment.onDestroyView()");
+        messageListAdapter.setOnContactPictureClicked(null);
+        messageListAdapter.setOnContactPictureLongClicked(null);
+        messageListAdapter.setOnQuoteListener(null);
+    }
 
     @Override
     public Animator onCreateAnimator(int transit, boolean enter, int nextAnim) {

src/main/java/eu/siacs/conversations/ui/ConversationsOverviewFragment.java

@@ -121,6 +121,21 @@ public class ConversationsOverviewFragment extends XmppFragment {
         }
     }
 
+	@Override
+	public void onDestroyView() {
+		Log.d(Config.LOGTAG,"ConversationsOverviewFragment.onDestroyView()");
+		super.onDestroyView();
+		this.binding = null;
+		this.conversationsAdapter = null;
+	}
+
+	@Override
+	public void onDestroy() {
+		Log.d(Config.LOGTAG,"ConversationsOverviewFragment.onDestroy()");
+		super.onDestroy();
+
+	}
+	
     @Override
     public void onPause() {
         Log.d(Config.LOGTAG, "ConversationsOverviewFragment.onPause()");