FeatureSummary: Refactor to use global properties for package types

These new global properties were added:

* FeatureSummary_PKG_TYPES: Package types accepted by FeatureSummary
  (default REQUIRED RECOMMENDED OPTIONAL RUNTIME).
* FeatureSummary_REQUIRED_PKG_TYPES: Package types that will cause
  FeatureSummary to abort when called with
  FATAL_ON_MISSING_REQUIRED_PACKAGES and a package in these categories
  is missing (default REQUIRED).
* FeatureSummary_DEFAULT_PKG_TYPE: Default package type assigned when
  not explicitly assigned by the user (default OPTIONAL).

This allows to add and remove new package types that can be printed
selectively using the "WHAT" argument.