Preset templates are sometimes set automatically

[svetogam]

This is the same issue for preset templates as for sub-routines in #6.

Cases:

1. Add 2 templates, select one of them in an Export Project from Template task, then delete that template. This changes the template in the task.
2. When there are no templates, add an Export Project from Template task, then add a new template. This sets the task to use the new template.

This can cause accidentally exporting with a template that the user never set. The same solution as for sub-routines should be fine.