Adds output formats list to items/show view.

Omeka provides links to its various output formats on the items/browse view.
(This was added in ae45808 in response to ticket #373.) Those same formats
are also generated for individual items. This change simply adds links to
those views on the core items/show view.
Adds output format list to items/browse.
Merge pull request #511 from clioweb/output-list-items-show

Adds output formats list to items/show view.