Clean up progress bar handling in BlogActivity
BlogActivity uses a ViewPager with two FragmentStatePagerAdapters, one of which contains a single BlogFragment (which in turn contains its own RecyclerView adapter) and the other a series of BlogPostFragments. The two adapters allow the blog to be viewed either as a feed or one post at a time.
The BlogFragment uses the RecyclerView's progress bar, whereas the BlogPostFragments rely on a progress bar in the BlogActivity. This complicates the interaction between the components and leads to a small bug when the BlogPostFragments are loading their posts: the progress bar is hidden when the first fragment finishes loading, even if the currently visible fragment is still loading.
Clean this up by moving the progress bar into the BlogPostFragment.
We should investigate other code that uses
BaseFragmentListener#show/hideLoadingScreen() for similar problems. We may be able to simplify the interaction between components by making each component responsible for showing its own progress bar.