Rework test/debug image features and crosssdk image definitions

Rework test/debug image features and crosssdk image definitions

Changes include:
- The agl-test-wgt/agl-devel-wgt image features and the scheme of
  appending to their FEATURE_PACKAGES definitions turned out to be
  problematic with respect to resulting in unexpected extra packages
  ending up in agl-image-{minimal,ivi}, etc., when building with
  agl-demo configured (which is typical usage). To avoid this, the
  FEATURE_PACKAGE definitions for the image features have been
  replaced with tweaks to define COMPLEMENTARY_GLOBS for the features
  to bring in the test/debug/coverage packages via that mechanism.
- The above removes the need to define the extra test/devel
  packagegroups, and requires some minor tweaks to aglwgt.bbclass to
  use a -debug package for the debug widget instead of -dbg, to avoid
  collisions with the dbg-pkgs image feature. As well, the afb-test
  package has been added as to RDEPENDS of all test widget packages,
  since that seems sensible and avoids needing to explicitly adding
  it elsewhere.
- Attempt to rework the various crosssdk image definitions to use a
  layered set of .inc files to remove duplication and ensure that
  additions to the SDK are declared once in the appropriate profile.
  It is likely that a clean sheet implementation would have some
  things coming from meta-agl-profile-graphical, so further rework
  may be required/desired to continue cleaning things up.

Bug-AGL: SPEC-3300, SPEC-3375

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I942b61501beb41d037001b70a501f90b9a59c45d