Simplify build modes

At present the module implements two build modes, a teaser and full node mode - however it only ever uses teaser. Further the naming of the build modes can cause confusion when attempting to use other modules that interact with build modes such as Views Attach. The build modes provided by the module are indistinguishable from the default full and teaser modes.

This patch retains the teaser mode which is currently being used for backwards compatibility, removes the full mode, and re-titles teaser to "Node as Block" so it's easy to distinguish when needed.