Grid bookmarklet

![gridshot](https://github.com/guardian/frontend/diff_blob/7146814b3f3ad5f906cc895176ec302d47c67b39/tools/grid-bookmarklet/screenshot.png)

A quick dev bookmarklet to overlay the NextGen grid on the current page

### Keyboard shortcuts
- **G**: Hide/Show grid 
- **D**: Desaturate content area
- **Arrow keys**: precise positioning *(hold Shift for larger increments)*

Create a bookmark with the following code:
```
javascript:(function()%7Bdocument.body.appendChild(document.createElement('script')).src='https://rawgithub.com/guardian/frontend/grid-bookmarklet/tools/grid-bookmarklet/grid.js?'+(new Date()).getTime();%7D)();
```