Publish remaining Platform and Sdk extensions

Currenly the repo at http://cache.sdk.freedesktop.org/releases/ contains the org.freedesktop.Platform image and the corresponding .Sdk image only. It does not contain any of the extensions defined in sdk.bst.

For my use case I need org.freedesktop.Platform.Icontheme, there are various others which will be needed too such as Sdk.Debug, Platform.GL, etc. Each of these needs to be built and pushed to the repo separately. Not all of them have corresponding .bst files yet, although some do (Sdk.Debug is defined in sdk-debug.bst for example).