Merge Logo control into Attribution

And make it collapsible to save some space.

Collapsed, by default:
![capture decran 2014-06-03 a 16 24 22](https://cloud.githubusercontent.com/assets/21686/3161365/1662e37a-eb2b-11e3-9e8e-14a60b9fa90e.png)

Opened when clicked, or with `collapsed: false`:
![capture decran 2014-06-03 a 16 24 31](https://cloud.githubusercontent.com/assets/21686/3161370/1bd9d160-eb2b-11e3-8af0-0f8ce62c29ea.png)

Uncollapsible, with `collapsible: false`:
![capture decran 2014-06-03 a 16 24 41](https://cloud.githubusercontent.com/assets/21686/3161380/22ebc832-eb2b-11e3-9320-57b31c29ce5e.png)

Examples using OSM sources have been updated not to collapse attributions, see [OSM copyrights](http://www.openstreetmap.org/copyright), and the API doc for attributionOptions links to OSM copyright.