Update all preferences when the account preference updates UI

When an account is added or removed, the account preference controller
just updates the account list, whereas there's no trigger point for the
account data sync preferences to refresh.

Add an API to update all preferences in DashboardFragment, so we can
refresh the account sync preferences whenever the account list is
updated.

Bug: 185479221
Test: robotest, manual
Change-Id: Ide3d972abae09ce0175e3bafbb1f4a5e307d20c8