Remove and refactor local greys from static

Update all instances of greys in static to use either semantic colour variables from the toolkit or nearest toolkit grey

• rationalised corresponding grey (see image attached)
• update to semantic variables
• update grey variables to match toolkit rather than static colours
• remove import of local colours.scss from application.scss
• delete _colours.scss

![greys](https://cloud.githubusercontent.com/assets/1692222/3952763/9dac0730-26e5-11e4-9121-714af25e5708.jpg)