Another styling pass for trading

for 
- overall consistency and spacing
- made the dropdowns look more like dropdowns
- in a saved pair state, the currency shouldn't look like a disabled dropdown, it should look more like it is static instead.
- some basic styling for widgets

![image](https://cloud.githubusercontent.com/assets/51415/4468113/a29ce824-48f8-11e4-8139-40854e9ef7a9.png)

I like to leave an empty line before nested styles to make the scss more readable and flatten compound selectors if only the inner-most block contains rules.

```css
border-radius: 2px;

li > a {
  padding: 10px 15px;
```