DialerStats: track how frequently contact images are present on the call detail page

For retail devices (and installer builds), introduce tags to be read
by a separate, additional, package.

This will not be read or collected in any community (nightly/M/etc) or
self-built build.

Change-Id: Ic06b09eb4667297abd44aa11b504088a91cd5102
Dialer: Remove unused strings

Change-Id: Id944ac3f7f4bb4b04e652120774a145f7349b848