Open file-choosers in last used location

[adamantivm]

This is a low priority ticket, but I add it anyways since it could be useful for others and we might want to remember about it.

Currently most file choosers start in ~/.ros Nevertheless, many times while composing complex scenes or working with multiple of them you need to repeatedly go dig into a sub sub sub directory to find your objects. It would save a lot of time if the file chooser remembered the last chosen location so that the next file can be picked up quickly