Allow control over disk image location

First of all, thanks for making this app! Having a virtualized linux on ARM architecture is very helpful for my work.

But I would have liked to be able to customize the location of the disk image files, for at least two reasons:

* Be able to cleanup orphaned files. The Library folder tends to accumulate a lot of waste on a Mac that has been running for years. This is not so much of a problem for most data, but when having disk image files at > 20Gb it does become a problem.
* Easy exclusion from backup software. I really don't want these files to be backed up, neither to my on-site time machine, nor my secondary cloud base backup solution.

I would kinda argue, that virtual disks is for virtualization software a bit like document files for a word processor, the user should have full control over their location.

Also, finding the files is not easy, I couldn't find anywhere in the app, that actually displays the file location. It took a google search to learn where they are located, so I could add the backup exclusions.