Options can be hidden and shown

This makes coinmap usable on mobile phones.

The site was unusable on my mobile (1280x780) because at least half the screen was taken up with additional information (see image below).

This pull request adds a basic toggle for the layers, making most of the screen as visible map rather than menus. The goal was to set the foundation toward a proper mobile navigation bar. which will make it easy to add new options (eg a filter by type such as bar, cafe etc).

![coinmap mobile screenshot](https://cloud.githubusercontent.com/assets/1281387/2675887/9e5e2aca-c126-11e3-8203-b651cf62380b.png)