Make voicemail notifications working.

A recent change in voicemail content provider set the mime type to
vnd.android.cursor.item/voicemail for individual voicemail records. But
the NEW_VOICEMAIL receiver's intent filter in contacts app manifest did
not have any mimeType set. So even before the content provider change,
this only used to work for voicemails with no audio data.

Fixed the manifest file to set correct mime type.

bug: 5141120

Change-Id: I03ce4146aa0962db1f4cbc25f755797d81df0469