[DO NOT MERGE] Use tokens instead of account access trackers

We keep track which process saw and account to whitelist
the app for future access as an optimization to avoid
prompting the user for account access approval. Some apps
use SefeParcelable where the parcels are marshalled
which does not allow the parcel to contain IBinders.
To avoid this we are switching from account tracker remote
objects to unforgeable tokens.

bug:31162498

Change-Id: I3b52bff720655f695ad0c58d420eb35ef93161b9