Add 'Previous Page' button to the App Catalog page

Also refactor a bit how detecting whether there are more Apps
works - to reduce code duplication and simplify it a bit.

Change-Id: I3601ebaaf18dfbca40430e9b1b0b6fdf5250498a
Implements: blueprint normalize-dashboard-pagination
Merge "Add 'Previous Page' button to the App Catalog page"