Add support for saving and opening files in the cloud, using the

syncFileSystem API.

!["Open in Cloud" dialog](https://f.cloud.github.com/assets/1071986/1356605/2f267b42-377b-11e3-8034-7b8b62609d97.png)

!["Save in Cloud" dialog](https://f.cloud.github.com/assets/1071986/1356608/447859e8-377b-11e3-8ea8-b13d510ac3ed.png)

!["Save in Cloud" overwrite prompt](https://f.cloud.github.com/assets/1071986/1356609/4faa4cae-377b-11e3-836f-563648a1dcdb.png)