Use telephony voicemail notification settings for vvm.

Previously visual voicemail notifications did not align with the
telephony voicemail notification settings that the user could visit
through dialer settings. After adding an API to access those telephony
settings, dialer can now read those settings and use them when providing
notifications for visual voicemail.
Also provide a VoicemailNotificationSettingsLookup class to enable
separate functionality for N and pre-N.

Bug: 24164917
Change-Id: I45d746b485be2f1db90b66a96885ba1485743b49