Add a shrink agl-demo-platform version

Hi, wminer jsmoeller

Could you give some advices, thanks.

Purpose:

Base on agl-demo-platform, make a shrink version for low performance board can run agl-demo-platform. We keep HOMESCREEN, HVAC, DASHBOARD and SETTING(vehicle correlation), remove other APPs and some services. Other apps can be customized by OEM and Tier1.

Method:

• Add a file agl-demo-minimal.bb to folder meta-agl-demo/recipes-platform/images 

• Add a file packagegroup-agl-demo-minimal.bb to folder meta-agl-demo/recipes-platform/packagegroups. 

• In order not to affect the original recipe file, packagegroup-agl-demo-minimal.bb include all recipe files that we need.agl-demo-minimal.bb packagegroup-agl-demo-minimal.bb