Replace ActivityInstanceInfo api with in app lifecycle event tracking

Since adding a public api for the playground app was problematic,
we now keep track of onResume and onDestroy calls globally inside the
app. This fixes a few bugs in cases where tasks would be hidden from the
ActivityManger#.getAppTasks() method and allows us to listen for changes
allowing us to do without a periodic refresh of the UI.

Test: Manual

Change-Id: Idb834cbdc7aad6442dd962c95b5321e1d75695fe