Allow browsing through the session folder

[ivoflipse]

Given I now display folders in Session folder, it would be nice if you double clicked a folder, that it would navigate into that folder.

This probably also requires your to be able to navigate up/back to its parent and/or go back to the default folder (as stored in the settings).

[ivoflipse]

You can now double click on folders and it will navigate to them.

I also added two buttons:

• Move back up to the folder you came from.
• Move back to the default folder (see settings)