In addition, added a @Nullable constraint on the categorySpinner
and a null guard when resuming the fragment to handle possible
null cases (though I don't think there will be any).
This caused the entire list view to e animated when navigating
back to the Available tab. Tried switching the `animateLayoutChanged=true`
to a child view only containing the category spinner, but this is not how
the animation handling works. It needs to animate both the thing being
hidden/shown, and also the next sibling of that thing to work properly.
Thus, moving the spinner to its own child and leaving the list didn't work.
There is no layout .xml file for the updated/installed list,
but there is for the available apps list. As a result, the `TextView` containing
the empty list message is added dynamically. With the recent improvements to
the category spinner, a `RelativeLayout` was used instead of a `ListView`. To
remedy this, the layout has been augmented to ensure the dynamically added
`TextView` still displays correctly.
