allscenarios-image-*-dev: Add devel/dbg image.

Looking at allscenarios-image-common.inc I see some devel/dbg packages
in there. These really should be pulled into a development or debug
image as images that endusers would build off of for a production
environment should only contain the minimal packages needed to run the system.

This patch removes gdbserver and packagegroup-net-tools (iperf3) from common
and puts them along with other useful EXTRA_IMAGE_FEATURES into two new images:

allscenarios-image-base-dev
allscenarios-image-extra-dev

Due to the size of the dbg-pkgs and dev-pkgs,
allscenarios-image-extra-dev needs a bump of it's ROOT_PARTITION_SIZE
else wic creation explodes.

Closes <issues 123>

Signed-off-by: Eilís Ní Fhlannagáin <elizabeth.flanagan@huawei.com>