Do not show "Show voicemail only" if no source is installed.

The "Show voicemail only" (and matching "Show all calls") options menu
items only make sense if there is at least one voicemail source
installed.

If not, then we should not show these options.

In order to determine whether a source is available, we use the
voicemail status table, which contains information about the installed
sources.

Bug: 5216976
Change-Id: Ib25aebba8509a1dd4c1c6de7cba2244461c69cfc