be able to create folders from the file browser

_From [st...@sprixelsoft.com](https://code.google.com/u/105605591483612568850/) on April 30, 2013 18:35:57_

When saving a new file, it would be handy if you could create a new folder within the file browser interface.

_Original issue: http://code.google.com/p/aseprite/issues/detail?id=233_
