Reclaim unused credits from unused apps.

Apps will start to lose 10% of their allocated ARCs every 24 hours after
72 hours of no use. However, we make sure not to take the app's balance
below the min balance as indicated by the EconomicPolicy.

Bug: 158300259
Test: Android builds
Change-Id: I55c7d74e5748a07965bee81df08855726e8b1660