Add view type list dropdown and 'brief' view

Closes #25, #40 

* Adds new `brief` search result view
* Adds preview to brief view
* Replaces button group view types with dropdown

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![image](https://cloud.githubusercontent.com/assets/302258/3330119/6148a90c-f7cd-11e3-8788-48db2a9d0bdc.png)
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![searchworks-issue40-1](https://cloud.githubusercontent.com/assets/302258/3330184/09e6f730-f7ce-11e3-8410-7835816c29fc.png)
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![image](https://cloud.githubusercontent.com/assets/302258/3330123/6cc95d26-f7cd-11e3-8436-3b18c9add8a2.png)



Similar to comment on `spec/features/brief_view_spec.rb`. Shouldn't the feature test be testing whether the button takes you to brief view rather than linking to it directly?