[Feature Request] Add command to open file location

Please add a way to open the directory currently pointed to by a file. Ristretto is not always opened by double-clicking an image file. For example, in Minecraft when you take a screenshot, it gives a link to the screenshot. When you click on it, Ristretto opens but users aren't given a clear location where the current file is located.

Options:

• Add a button on the command bar to open current picture location
• Add a entry to the right-click menu on a picture
• Add "Open file location" option to the File menu.

Thanks for a great program!