Add overview button handling to Go recents.

Add the same overview button handling as in the original launcher.
Specifically, pressing overview on recents will launch the next
appropriate task (e.g. the next most recent task if you came from an
app).

Bug: 114136250
Test: Go to recents from launcher, press overview => launch task.
Test: Go to recents from app, press overview => launches next task
Change-Id: I946974b4c2b65b6d0f212d8e8c0816983386d952