BUG: create correctly named indexables in HDFStore Tables
- indexable columns were created and named in a legacy format, now named like the
  indexable in the object, e.g. 'index' for DataFrame, or 'major_axis'/'minor_axis' for Panel
- fixes an issue if we want to support say a 'column' oriented Table
   (e.g. instead of storing the transpose,
  store with a 'column' indexables) - not implemented yet, but supported now
