Tweak agl-profile-graphical packagegroups

To more easily allow using Weston in profiles derived from
agl-profile-graphical, rename packagegroup-agl-image-weston to
packagegroup-agl-graphical-weston and tweak the definitions of it and
packagegroup-agl-profile-graphical so that non-Weston related packages
are only included via from packagegroup-agl-profile-graphical.  The
contents of agl-image-weston and agl-demo-platform remain unchanged
after these changes.

Bug-AGL: SPEC-1730

Change-Id: I4915bb896cc11ea49103400795a65c92b5889110
Signed-off-by: Scott Murray <scott.murray@konsulko.com>
(cherry picked from commit 4f7222e10cbe09ea3231eab912857fc7ba9d1c12)