Add import for SEND_TO_VOICEMAIL.

+ Add utility class for async import functions.
+ Move check for contacts with SEND_TO_VOICEMAIl to util.
+ Add function for adding phone numbers of contacts with
SEND_TO_VOICEMAIL to the block list, then clearing the
SEND_TO_VOICEMAIL flag.
+ Fixed bug where the import text would not be shown for an empty
block list. Rearranged layouts slightly to facilitate this.
+ Protect against null listeners in FilteredNumberAsyncQueryHandler.

Bug: 23351616
Change-Id: Id526e16f20a3d28966bbc5e458cecfcd03ecb20f