Add better support for VM Templates

For my current workflow I plug into the utmctl command line interface. But every now and then I need to open the utm interface to remove a still running VM.

The following features might help with a template vm and clones from it:
1. Allow to tag a VM as template:
- prevent power on without warning (so the template is not edited without a user specifically wanting to do that)
- prevent deletion without warning (so the template is not removed without a user specifically wanting to do that)
3. If you clone a vm and a vm with that name already exists, add a identifier to the end of the name so you can differentiate both (a bit like duplicate files in Finder for example) - through utmctl you can set a name but it does not check for uniqueness
4. Allow to force stop and remove a vm with one command in utmctl.

I can give more info on the reasoning behind this if wanted and share more info on my setup. (I use utm to do automation testing with ansible mainly).