docs: Updated layout and timestamps of developer stories.

The developer stories for Aftenposten, El Mundo, Segundamano, Tapps,
and Upbeat Games now appear closer to the beginning/top of a section
on the newly-formatted "latest" page.

Also, Tapps and Upbeat Games now appear within the "games" section,
not the "apps" section. The Glu case study also appears within the
"games" section; it was incorrectly appearing under the root
"stories" directory before.

Finally, removed a duplicate case study describing Dots increasing
installs using Store Listing Experiments.

Bug: 29240693
Change-Id: Ieec3afd2f56320da00ee4b97d8cd8de8253784dd