Disk Image Mounter
The Gnome Disk Utility is a tool to manage disk drives and media. You can install inside a terminal with this command:
sudo apt-get install gnome-disk-utility
This should add 'Disk Image Mounter' to the context menu when right-clicking the ISO file.
In Nautilus right click on a ISO file and the first choice in the context menu is "Open with Archive Mounter".