Tidy spacing around search box / add hover state

- Toggle checkbox filters don't have a hover state, which they should do as they are clickable
- The padding around the searchbox (it is different to the padding around the other form elements...) has always driven me crazy so I've fixed it.

before:
![screen shot 2014-07-01 at 10 10 44](https://cloud.githubusercontent.com/assets/68009/3441723/ba83d6f6-0108-11e4-92c4-84d84ce65c18.png)

after:
![new](https://cloud.githubusercontent.com/assets/68009/3441734/dee08828-0108-11e4-8947-bb5c62d5f116.png)