Add deselect to batch selection mode

src/org/thoughtcrime/securesms/ConversationListAdapter.java

@@ -69,8 +69,12 @@ public class ConversationListAdapter extends CursorAdapter implements AbsListVie
     }
   }
 
-  public void addToBatchSet(long threadId) {
+  public void toggleThreadInBatchSet(long threadId) {
-    batchSet.add(threadId);
+    if (batchSet.contains(threadId)) {
+      batchSet.remove(threadId);
+    } else {
+      batchSet.add(threadId);
+    }
   }
 
   public Set<Long> getBatchSelections() {

src/org/thoughtcrime/securesms/ConversationListFragment.java

@@ -106,7 +106,7 @@ public class ConversationListFragment extends SherlockListFragment
                                  headerView.getDistributionType());
       } else {
         ConversationListAdapter adapter = (ConversationListAdapter)getListAdapter();
-        adapter.addToBatchSet(headerView.getThreadId());
+        adapter.toggleThreadInBatchSet(headerView.getThreadId());
         adapter.notifyDataSetChanged();
       }
     }
@@ -146,7 +146,7 @@ public class ConversationListFragment extends SherlockListFragment
         batchMode  = true;
 
         adapter.initializeBatchMode(true);
-        adapter.addToBatchSet(((ConversationListItem) v).getThreadId());
+        adapter.toggleThreadInBatchSet(((ConversationListItem) v).getThreadId());
         adapter.notifyDataSetChanged();
 
         return true;