Refactored VoicemailContentProvider to simplify using multiple tables.

This is needed to simplify the voicemail provider to be able to serve
operations on the voicemail_status table as well.

The idea is to retain all common functionality related to voicemail
permission check etc in the main VoicemailContentProvider class. And
delegate database level operations to another class that only deals with
functionality speficic to the underlying table.

In the favor of code reuse the interaction between voicemail_content_provider
and voicemail_table_implementations is both ways. VoicemailTable
interface defines the operations exposed by both sides.

I have also added a couple of new test cases to cover getType() and
source_package check in the uri. Old test cases continue to pass to
prove that the refactoring did not break any functionality.

Change-Id: I4cb031234c2f5746084c51557e2ba0edbaf3d6de
4 files changed