Add CUSTOM_NOTIFICATION to ContactsContract to allow custom notification sounds to be assigned to individual contacts - picked from here: https://github.com/UltimatumKang/android_frameworks_base/commit/36d850394ede7db15023fe538c1b3d541d16cec5

Change-Id: Iba40e5237200385a467ac9cdb441b1ed7de3a1da