Widget packaging rework

Changes include:
- Add "agl-test-wgt" to IMAGE_FEATURES in the agl-demo template
  definition to yield the desired default behavior of the test
  widgets always being added to the agl-demo-platform image.
- Created new devel and test packagegroup variants for several of the
  existing packagegroups to contain the associated widgets.
- Added several services to the RDEPENDS in the definition of
  packagegroup-agl-ive-services that have been getting picked up by
  application RDEPENDS. This simplifies the test/devel packagegroup
  definitions.
- Extend the agl-devel-wgt and agl-test-wgt FEATURE_PACKAGES
  variables as necessary to add the required corresponding widget
  packagegroups.
- Shifted some non-applications and the use of
  packagegroup-hmi-framework around a bit in the definition of
  packagegroup-agl-demo-platform to improve clarity.
- The alexa-viewer app and virtual/alexa-voiceagent-config package
  are now pulled in by extending the agl-voiceagent-alexa
  FEATURE_PACKAGES definition. This is a cleaner use of the image
  feature than the previous checking of IMAGE_FEATURES that was being
  done in the packagegroup-agl-demo-platform definition.

Bug-AGL: SPEC-3300

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I0ace2d140fdceb1e0d778a0fe71d7f856a953ae4