update string filter UI

+ removes "Search %{field}" translations since as of #2096 you get to choose the search method
+ updates string filter UI so the method select is side-by-side with the input field
+ moves related JS out of the HTML

Before
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![string_filter_before](https://f.cloud.github.com/assets/688886/564761/57cd979e-c5a0-11e2-8c20-5cc646df4acb.png)
After
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![string_filter_after](https://f.cloud.github.com/assets/688886/564762/5fc6937e-c5a0-11e2-9645-aad00ed7eb54.png)