AccountListAdapter: Extend BaseAdapter instead of implementing ListAdapter - remove the registerDataSetObserver and unregisterDataSetObserver methods
AccountsActivity: Store reference to AccountListAdapter and call notifyDataSetChanged on the adapter in onResume, to have the list refresh itself. When new account is created, the list will then automatically display the new account.
FacebookAccount: Add TODO in FacebookAccount - check for invalid input in constructor
FacebookAccount: Add a TODO in getDisplayName