Add a generic account chooser/add account flow for apps.

The activity is launched as follows:
  Account account1 = new Account("account1@gmail.com", "com.google")
  Account account2 = new Account("account2@gmail.com", "com.google")
  ArrayList<Account> accounts = new ArrayList<Account>();
  accounts.add(account1);
  accounts.add(account2);
  String[] accountTypes = new String[]{"com.google", "com.android.exchange"};
  Bundle addAccountOptions = null;
  Intent intent = AccountManager.newChooseAccountIntent(account1, accounts,
    accountTypes, addAccountOptions);
  startActivityForResult(intent, 0);

Change-Id: I05a467bdc3552a2e39397b0182879351f4324389