Prevent empty state messages from showing briefly

When we clear a list in onPause(), the proper behavior is that the empty state
message is shown, because the list is indeed empty.

However, we will reload the list content again in onResume(),
so the fix chosen in this commit is to force showing the progress bar
right after clearing the list.

Closes #576

briar-android/src/org/briarproject/android/blogs/MyBlogsFragment.java

@@ -82,6 +82,7 @@ public class MyBlogsFragment extends BaseFragment {
 	public void onResume() {
 		super.onResume();
 		adapter.clear();
+		list.showProgressBar();
 		loadBlogs();
 	}
 

briar-android/src/org/briarproject/android/contact/ContactListFragment.java

@@ -192,8 +192,9 @@ public class ContactListFragment extends BaseFragment implements EventListener {
 	@Override
 	public void onPause() {
 		super.onPause();
-		adapter.clear();
 		eventBus.removeListener(this);
+		adapter.clear();
+		list.showProgressBar();
 		list.stopPeriodicUpdate();
 	}
 

briar-android/src/org/briarproject/android/forum/ForumListFragment.java

@@ -119,6 +119,7 @@ public class ForumListFragment extends BaseEventFragment implements
 		super.onPause();
 
 		adapter.clear();
+		list.showProgressBar();
 		list.stopPeriodicUpdate();
 	}
 

briar-android/src/org/briarproject/android/introduction/ContactChooserFragment.java

@@ -140,6 +140,7 @@ public class ContactChooserFragment extends BaseFragment {
 	public void onPause() {
 		super.onPause();
 		adapter.clear();
+		list.showProgressBar();
 	}
 
 	@Override

briar-android/src/org/briarproject/android/sharing/InvitationsActivity.java

@@ -28,6 +28,7 @@ abstract class InvitationsActivity extends BriarActivity
 			Logger.getLogger(InvitationsActivity.class.getName());
 
 	private InvitationAdapter adapter;
+	private BriarRecyclerView list;
 
 	@Inject
 	protected EventBus eventBus;
@@ -40,8 +41,8 @@ abstract class InvitationsActivity extends BriarActivity
 
 		adapter = getAdapter(this, this);
 
-		BriarRecyclerView list =
-				(BriarRecyclerView) findViewById(R.id.invitationsView);
+
+		list = (BriarRecyclerView) findViewById(R.id.invitationsView);
 		if (list != null) {
 			list.setLayoutManager(new LinearLayoutManager(this));
 			list.setAdapter(adapter);
@@ -60,6 +61,7 @@ abstract class InvitationsActivity extends BriarActivity
 		super.onPause();
 		eventBus.removeListener(this);
 		adapter.clear();
+		list.showProgressBar();
 	}
 
 	@Override