Previously, navigating back to an app which is in the queue
qould indeed grey out the "Install" button and show the text
"Downloading..." in that disabled button. However, it woulnd't show
any sort of progress. This change shows an indeterminite progress
bar with the text "Waiting to start download..." underneath.
Happy to receive input on the best terminology if that is not
desirable.
In order to do this, I had to be more specific about when
the header fragment is updated. Previously, `headerFragment.updateViews()`
would get called by the `onResumeFragments()` activity method.
This was redundant because the `onResume()` method of the fragment
also invokes `updateViews()`. Thus, that call was removed (though
we still need to obtain a reference to the fragment in
`onResumeFragments()`.
18f3d86b68