Rename docker worker containers and reduce size

docker-worker-generator is used to generate docker containers that can be used for platform development (fully rebuild AGL platform) or for applications development (build an app or a service based on AGL SDK).

So I propose to rename images as follow  

docker.automotivelinux.org/agl/worker-generic  ==> docker.automotivelinux.org/agl/platform-devel

docker.automotivelinux.org/agl/worker-xds ==> docker.automotivelinux.org/agl/application-devel

Moreover X11 and documentation tools/utilities are install by default and are rarely used.
So I propose to not install them by default and add scripts inside container (eg. /home/devel/
additional_install/x11_tools.sh) that can allow user to easily install those tools manually if he really need them.