Add CMake feature and dependency summary

Use CMake's standard package discovery output and FeatureSummary instead
of custom status messages, so configuration reports package
availability, versions, and failure reasons consistently. Rename Ceres
feature controls to use the WITH_ prefix to group them consistently and
eliminate inconcistent naming. Remove retrospective cache updates so
package discovery preserves caller-provided values and avoids
unnecessary side effects.

Fixes #876

Change-Id: Ib6e40d56a0ea89b292fe34554777593ffda95f42