Remove duplicate display name

The ServiceObject#display_name code was duplicated on three places, so the first patch takes care of dedup.

Second patch encapsulates the barclamp catalog YAML access into BarclampCatalog class. The ServiceObject still contains 'proxy' methods (e.g run_order, barclamp_catalog), as some barclamps (Nagios) rely on them. After they're fixed, these methods can be safely removed.

The last patch fixes the references in the crowbar barclamp itself.

Tested by running an install and loading the pages whose controller actions access the catalog.