No apps should appear in both lists

No apps should appear in both the 'Latest' and 'Updated apps' lists.

It brings in a function 'featureable()' to ascertain whether an app should be "featured" prominently at all. If not 'featureable'then the app will not appear in either list. This might be useful for some apps, moving forward. For example I have moved the test for whether an updated app has a "What's New" message into this featureable() function.