Adds side navigation in record view

Closes #374 

* Enables side navigation bar when record view page has scroll bar (for MARC and MODS objects)

Moved all repeating ids and icon tags to `searchworks.en.yml` for ease of maintenance

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![image](https://cloud.githubusercontent.com/assets/302258/3741087/454808d4-175c-11e4-8eba-1b18c22dc9ad.png)

This is essentially the same pattern as we follow w/ the sections themselves, although it seems like we've added an additional layer of abstraction which could cause confusion.

One way to clean this up a bit would be to change the `has_contents_summary` if statement below to something like:

    <% if (contents_summary = render "catalog/record/marc_contents_summary" ).present? %>
    ...

You could then construct the locals after all the metadata sections by referencing the variables (and if they're present or not).

    locals = {
      type: 'marc',
      has_data: {
        contents_summary: contents_summary.present?,
        ...
      }
    }