Add $type property to PhabricatorTypeaheadCommonDatasourceController

Summary: Fix an implicit property.

Test Plan: No more [11-Oct-2012 14:44:26] WARNING: [pool www] child 72785 said into stderr: "NOTICE: PHP message: [2012-10-11 14:44:26] PHLOG: Wrote to undeclared property PhabricatorTypeaheadCommonDatasourceController::$type. at [/INSECURE/devtools/phabricator/src/aphront/AphrontController.php:65]"

Reviewers: vrana, btrahan

Reviewed By: vrana

CC: aran

Differential Revision: https://secure.phabricator.com/D3685