Widget packaging rework

Widget packaging rework

Changes include:
- Created new packagegroup-agl-speech-services packagegroup and
  associated test and devel packagegroups to replace previous
  extending of packagegroup-agl-ivi-services via bbappend.
  This makes it simpler to create the test/devel packagegroups
  in packagegroup-agl-ivi-services, and is cleaner with respect to
  the packagefeed since it avoids modifying a packagegroup in another
  layer.
- Extend the agl-devel-wgt and agl-test-wgt FEATURE_PACKAGES
  variables as necessary to add the required corresponding widget
  packagegroups.

Bug-AGL: SPEC-3300

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I17b61f3e4549a7baa8ac1a6f9c857e2f78bb6448