Extend BlogActivity to also show individual posts

This allows for swiping left/right to read other posts by using
a ViewPager.

This hasn't been done as a separate activity, but with
fragments, so both can share the `BlogPersistentData` without
needing to reload it.

Closes #428

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

@@ -0,0 +1,29 @@
+package org.briarproject.android.blogs;
+
+import android.support.annotation.Nullable;
+
+import org.briarproject.android.controller.ActivityLifecycleController;
+import org.briarproject.android.controller.handler.UiResultHandler;
+import org.briarproject.api.sync.GroupId;
+import org.briarproject.api.sync.MessageId;
+
+import java.util.TreeSet;
+
+public interface BlogController extends ActivityLifecycleController {
+
+	void loadBlog(final GroupId groupId, final boolean reload,
+			final UiResultHandler<Boolean> resultHandler);
+
+	TreeSet<BlogPostItem> getBlogPosts();
+
+	@Nullable
+	BlogPostItem getBlogPost(MessageId postId);
+
+	@Nullable
+	MessageId getBlogPostId(int position);
+
+	interface BlogPostListener {
+		void onBlogPostAdded(final BlogPostItem post, final boolean local);
+	}
+
+}