Add a directory selector when creating/saving files

[dclong]

Currently an user have to manually type the path if he wants to create/save files in/to a different directory rather than the current one.

[ellisonbg]

Adding a full blown file/directory browser to the save dialog add a ton of complexity to the UX. We are trying hard to not go down that path. The only way I could imagine doing this in a seamless manner is to allow directories to be typed into the file name, similar to how GitHub's online editor works. So if you type ../name.txt is moves it up one.