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Add decorated partial magic for asset view

- Adds a SolrDocument decorator for going from document to its viewer.
- Adds views to handle viewers, though most are just dummy views for
  now to get this working
Add specs to verify asset viewer selection
Added suggestion for implementation of viewer decorators.
Extract catalog decoration into module

- Creates a new module specifically for decoration
- Loads document object from existing @document to avoid a double hit
  on the solr instance
- Caches the decorated object
Merge pull request #77 from OregonDigital/feature/viewer-partials

Feature/viewer partials