* generates mustache-ready alpine-mksite/cloud/release.yaml for new alpinelinux.org/cloud page
* rename old gen_releases.py to gen_releases-in.py (for old page)

cloud/
* convert_image() remove from AWS, generalize, and add to CloudAdapterInterface
* stub upload_image() and release_image() in CloudAdapterInterface

ImageConfig
* add properties: v_version, artifacts_yaml, image_file, image_path, upload_url, download_url
* rename image_url to to region_url

configs/
* drop 'builder' attribute, it's always 'qemu'
* add image_format, upload_path, download_path, and remote_path to Default block